Zen Water Purification, Filtration and Treatment

 

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Water Purification, Filtration and Treatment

 

Please read our Medical Disclaimer.

 

Staying hydrated is an extremely important aspect of survival, especially in hot environments.  One of the biggest enemies is is waterborne diseases that cause diarrhea.  A little bit of diarrhea can slow you down and ruin a trip while more severe cases of diarrhea can lead to severe and even life threatening dehydration.  In fact, waterborne diseases are the largest culprit of death and morbidity in the third world.

 

No matter where your treks take you, you should take water purity into consideration to avoid the miserable case of the poo poo butt.

 

Note: Information on this page was compiled many years ago.  Information found here may not be complete or up to date.  Some of this information may also have been sourced from textbooks with inaccurate information or based on studies which were flawed in some way.  Some of the products mentioned on this page are also no longer commercially available.

 

Harmful Microorganisms

Protozoa

Giardia lamblia

Cryptosporidium

Entamoeba histolytica

Cyclospora cayetanensis

Bacteria

Campylobacter jejuni

Viruses

Chemicals Toxins

 

Water Selection

Bottled Water

Tap Water

Ice Snow

 

Water Filters, Purifiers and Treatment

Filtration

Filter-Purifier_Designs

Hand Pump Filters

Gravity Filters

Bottle Filters

Sippy Filters

Reverse Osmosis

Purifiers

Flocculating Agents

Sedimentation

Prefiltering

Filter Membrane Construction

Boiling and Pasteurization

Sterilization

Pasteurization

Distillation

UV Radiation

Solar Photooxidative Disinfection

 

 

Chemicals

Chlorine Dioxide

Sodium Chlorite and Sodium Bisulfite Tablets

Sodium Chlorite and Phosphoric Acid Solutions

Stabilized Chlorine Dioxide Liquid

Chlorine

Bleach

Halazone tablets

Sodium dichloroisocyanurate

Superchlorination-dechlorination

Calcium hypochlorite

Chloramine

Chlor-Floc

Sodium thiosulphate

Iodine

Concentrated Alcoholic Iodine

2% Tincture of Iodine

5% Liquid Iodine

LifeSystems Iodine

Povidone-Iodine

Tetraglycine hydroperiodide

Iodine Crystals

Mixed Oxidants

Metal ions

Copper-Silver ionization

Silver Ions

Potassium Permanganate

Hydrogen Peroxide

Other Chemical Treatments

 

Choosing a Water Treatment System

Full Protection

Protection against Protozoa and Bacteria

Minimal Protection

 

References and Additional Information

 

 


Harmful Microorganisms

Most of the threats in water come from bugs originating from human or animal excrement, but other environmental threats now include chemicals and radioactive pollutants that may be present in your water.

 

Microorganisms that contaminate water often cause various degrees of abdominal discomfort and diarrhea.  The loss of fluids from diarrhea in turn can dehydrate victims significantly, sometimes to the point of incapacitation or even death.  Other microorganisms common in water cause other harmful effects to the body depending on the organism and other factors.  Waterborne illnesses are still the biggest cause of death and disease in the world and should be taken seriously when in the outback and traveling abroad.

 

The following is a list of some more common pathogens that backpackers may encounter in drinking water, but is in no way all inclusive.

 

Protozoa

These are single celled microorganisms including Giardia lamblia and Cryptosporidium parvum.  Also commonly lumped into the protozoan list are parasitic worms.  These are not protozoa but are in fact higher evolved multi-celled parasites.  Like parasitic protozoa, parasitic worms can be a real problem and are generally resistant to chemical treatments such as chlorine or iodine.  They can be filter out by a good quality filter or inactivated by boiling.

 Giardia

Giardia lamblia (aka beaver fever)

These parasites are some of the oldest forms of life on earth and one of the more common parasites that hikers may encounter in their water.  Their little hard shelled cysts wait for you downstream from where humans and other animals defecate.  Then once ingested, they use their suckers to attach to your intestines and begin their reign of terror.

 

Size:

Cell size: 10 to 20 μm. 

Cyst Size: 8 to 19 μm

 

Occurrence:

Worldwide

 

Causes:

Giardiasis (gastroenteritis)

 

Symptoms:

Diarrhea, abdominal cramps, bloating, fatigue, weight loss, flatulence, anorexia, and nausea, in various combinations.  Fever and vomiting are uncommon

 

Incubation:

Incubation period of 1 to 14 days (average of 7 days)

 

Duration:

Usually lasts 1 to 3 weeks but can become chronic, resulting in malabsorption

 

Treatment:

Metronidazole 250 mg three times a day for 5 days
Nitazoxanide 500 mg twice a day for 3 days

 

Protection:

Giardia cysts are relatively resistant to chlorine (see Back-country water treatment to prevent giardiasis. Jerry E. Ongerth, PhD), especially at higher pH and low temperatures.  Iodine has some effectiveness against Giardia but is not completely reliable.  Recommend water filter with pore sizes of 1 micron or less, boiling of water or UV light treatment.  MIOX and chlorine dioxide are also options but may require extended treatment times.

 

Cryptosporidium (aka Crypto)

Cryptosporidium hominis, Cryptosporidium parvum and other species of Cryptosporidium are single celled protozoa that can pose a problem to backpackers.

 

Size:

Oocysts 4 to 6 μm

 

Occurrence

North America, Europe, Latin America, Australia, and Asia

 

Causes:

Cryptosporidiosis

 

Symptoms:

Cryptosporidium enteritis: diarrhea, loose stool, cramps, upset stomach and often a slight fever.  Folks with weakened immune systems are at risk of developing cryptosporidiosis, which can become chronic and can be fatal.

 

Incubation:

Generally begin 2 to 10 days (average 7 days) after becoming infected with the parasite

 

Duration:

Symptoms last an average of 6-10 days but can last up to several weeks

 

Treatment:

Nitazoxanide 500 mg twice a day for 3 days

 

Protection

Cryptosporidiosis is poorly inactivated by chlorine or iodine disinfection. Recommend water filter with pore sizes of 1 micron or less, boiling of water or UV light treatment.  MIOX and chlorine dioxide are also options but may require extended treatment times.

 

Entamoeba histolytica (aka amebic dysentery, amebiasis)
Entamoeba histolytica is a nasty bug and is second to only malaria for protozoal cause of death. 

 

Size:

Trophozoites range may be 10 to 60 μm. 

Cysts range 10 to 20 μm

 

Occurrence:

Occurs worldwide but is more common in areas of poor sanitation and nutrition, particularly in the tropics.  The majority of E. histolytica infections, morbidity, and mortality occurs in Africa, Asia, and Central and South America.

 

Causes:

Amoebic dysentery

 

Symptoms:

It causes a breakdown of the host's tissue and can lead to amebic colitis, liver abscesses, rupture of lungs, brain abscesses and death.   The amebic colitis presents itself with fevers, weight loss, severe abdominal pain and bloody diarrhea.

 

Incubation:

Commonly 2-4 weeks but ranges from a few days to years

 

Duration:

Amebic colitis may last for several weeks.

 

Treatment:

Metronidazole 500-750 mg three times a day for 7-10 days

Tinidazole 2g once daily for three days

More severely effected victims may require hospitalization and in very severe cases will need surgery.

 

Protection:

Since this may be found in fecaly contaminated water in conjunction with pathogenic parasites, filtering alone is not recommended.  Questionable water should be avoided and if used should boiled or filtered and chemically treated.  UV light treatment may be of some benefit.

 

Cyclospora cayetanensis

Cyclospora is a potential problem in the summer and rainy season (mid-April through September) in Nepal.  It can cause explosive diarrhea and is resistant to iodine.  You my need to boil your water or use a filter if in Nepal during the summer or rainy season.

 

Size:

Oocysts are 8-10 microns in diameter

 

Occurrence:

Napal and other destinations

 

Causes:

Cyclosporosis

 

Symptoms:

Infects the small intestine (bowel) and usually causes watery diarrhea, with frequent, sometimes explosive, bowel movements. Other symptoms can include loss of appetite, substantial loss of weight, bloating, increased gas, stomach cramps, nausea, vomiting, muscle aches, low-grade fever, and fatigue.

 

Incubation:

Onset of symptoms averages 1 week

 

Duration:

May last for a few days to a month or longer

 

Treatment:

Trimethoprim/sulfamethoxazole DS twice a day for at least 7 days

Correct diagnosis is important since treatment differs from other protozoa

 

Protection

Highly resistant to iodine.  Recommend water filter with pore sizes of 1 micron or less, boiling of water or UV light treatment.  MIOX and chlorine dioxide are possible options but may require extended treatment time.

 

Other Significant Waterborne Parasites

Organism Disease
Acanathamoeba castellannii Amoebic meningoencephalitis
   
Ascario lumbricoides
  (round worm - Nematoda)
Ascariasis
   
Balantidium coli Balantidiasis  (dysentery)
   
Naegleria gruberi

  N. fowleri

Amoebic meningoecephalitis
   
Schistosoma mansoni Schistosomiasis
   
Taenia saginata
  (beef tapeworm - Cestoda)
Taeniasis

 

Bacteria

Bacteria such as E. coli, Campylobacter jejuni, salmonella, cholera and others many others can cause significant and even life threatening diarrhea or food poisoning.  They range in size between 0.2 and 10 microns.

 

Symptoms may appear within hours to days of ingestion and may last several days or longer (depending on organism).

 

Antibiotics treatment depends on the pathogenic organism and may be needed.

 

Most water treatment chemicals and fine filters (0.2 microns or less) are effective against bacteria.

 

Escherichia coli

Most E coli is relatively harmless in small concentrations but can be a major cause of travelers diarrhea and gastroenteritis.

 

The deadly E. coli often reported in the papers is a special strain.  E. coli O157:H7 is less common, but is becoming an emerging cause of foodborne and waterborne illness.  This strain produces a powerful toxin and can cause severe illness and even death.

 

Campylobacter jejuni

Campylobacter jejuni is a common wilderness bug.  Campylobacteriosis symptoms usually vanish within 5 days.

 

Other Significant Waterborne Bacteria

Organism Disease
Brucella melitensis Brucellosis (undulant fever)
   
Leptospira icterohaemorrhagiae
  (spirochaetales)
Leptospirosis (Wells disease)
   
Pasteurella tularensis Tularemia
   
Pseudomonas pseudomallei Melioidosis
   
Salmonella typhosa Typhoid Fever
  S. paratyphi
  S. schottinulleri
  S. hirschfeldi C.
Paratyphoid fever
   
Shigella flexneri
  Sh. dysenteriae
  Sh. sonnei
  Sh. paradysinteriae
Bacillary dysentery
   
Vibrio comma
  V. cholerae
Cholera

 

Viruses

Viruses are extremely small (0.004 to 0.1 microns) and can cause a great many diseases.  There are more than 140 enteric viruses known to infect humans waiting for you out there.  These include hepatitis A, rotavirus, Norwalk virus and poliovirus. 

 

Viruses found in contaminated water is usually from human fecal contamination and often have a short lifespan when exposed to UV light.  Because of this, they are less likely to be found in wilderness settings in first world nations.  However, they are much more common in less developed parts of the world and in more populated areas where where there is a constant supply of hosts and recontamination.

 

Most antimicrobials have no effect on viral illnesses and treatment is limited to systematic relief and hydration.  The best form of protection is avoidance of contaminated water, food and hands.  Hepatitis A (as well as typhoid) vaccination is a good idea for anyone planning on traveling abroad.

 

Water filters are not able to filter out these ultra small pathogens and they should be treated by boiling/pasteurizing water, with UV light or with chemical treatment.

 

Significant Waterborne Viruses

Organism Groups Diseases
Poliovirus Muscular paralysis, Aseptic meningitis, Febrile episode
   
Echovirus Aseptic meningitis, Muscular paralysis, Guillain-Barres Syndrome, Exanthem, Respiratory diseases, Diarrhea, Epidemic myalgia, Pericarditis and myocarditis, Hepatitis
   
Coxsackievirus Herpangina
   
Enterovirus A Acute lymphatic pharyngitis, Aseptic meningitis, Muscular paralysis, Hand-foot-mouth disease, Respiratory disease, Infantile diarrhea, Hepatitis, Pericarditis and myocarditis
   
Enterovirus B Pleurodynia, Aseptic meningitis, Muscular paralysis, Meningoencephalitis, Pericarditis, endocarditis, myocarditis, Respiratory disease, Hepatitis or Rash, Spontaneous abortion, Insulin-dependent diabetes, Congenital heart anomalies
   
Reovirus Not well known
   
Adenovirus Respiratory diseases, Acute conjunctivitis, Acute appendicitis, Intussusception, Subacute thyroiditis, Sarcoma in hamsters
   
Hepatitis Infectious hepatitis, Serum hepatitis, Downs Syndrome

 

Chemicals and other toxins

Water can be contaminated by any number or things.  Man made chemicals, radioactive waste, heavy metals or other pollutants caused by man can be found downstream of farms (fertilizers, pesticides, herbicides), factories, mines or any populated areas.  Radioactive waste in water can be found in some parts of the world and small amount can cause thyroid failure and other problems.  Toxic bacteria can grow in shallow water and cause all sorts of potential problems.

 

Charcoal filters are of limited value and there is no good way for treating polluted water.  Distillation of water can be used to separate many salts and heavy metals from water, but will not separate out many oils, petroleum, alcohol and similar substances.  Questionable water should be always be avoided.

 


Water Selection

The first step in getting safe drinking water is selecting water that is less likely to to harmful in the first place.

 

Bottled Water

Just because water is bottled, doesn't mean it is safe to drink.  Bottled water is only as safe as its source and it is not unheard of to find harmful microorganism in bottled water abroad.  Some locals will even take your used bottles, fill them with stream water, seal them and gladly resell them to you.  If purchasing water, try to procure name brand bottles from "reputable" shops and make sure that the caps are sealed. 

 

Carbonated water and drinks are a bit safer as the acid levels from the carbonation is enough to kill many of the bacteria that may be present in the water.  If bottled water in not available, you may wish to stick with carbonated beverages, beer, and wine while abroad.  The tops of drink cans and bottles should be wiped clean to remove any external moisture and dirt.  Ice, as temping as it might be, should always be considered contaminated.

 

Tap Water

Tap water may come for water treatment plants, wells or other sources.  In most cities in Western Europe and the US, tap water is generally safe to drink, though it may contain minerals, chlorine and other impurities that may taint its taste.  Microorganisms do occasionally contaminate public drinking water, though this is rare in developed countries.

 

In countries outside of the US and Western Europe, you should avoid drinking untreated tap water.  Even gargling or rinsing off your toothbrush with it can lead to some horrendous diarrhea.  Only use bottled or properly treated water for consumption and oral hygiene.

 

Wilderness Water

In alpine wilderness areas where there is little exposure to humans, many of the streams and water sources are free from man made pollutants and of many the pathogenic bacteria and viruses carried by humans and passed on via fecal contamination.  But even without the human threat, there are many natural threats that can cause potential problems to those drinking untreated or inadequately treated water.

 

Never use water that could be contaminated with chemicals, such as water downstream from any factories, mines or human populated areas.

 

Avoid water in areas of or downstream from sources of feces.  This includes areas where animals frequent.

 

Avoid water from areas where humans camp, bath, or where trails cross water.  Drinking water sources should be at least 100 feet (30 meters) away and upstream from latrines.

 

Turbulent water can mix up sediment and microorganisms that would otherwise sink and settle.  Because of this, some recommend selecting still clear water over flowing streams to avoid exposure to Giardia cysts.  On the other hand, stagnant water should be avoided since it may contain toxic levels of toxic algae.

 

Pools of water without any green vegetation growing near it or animal remains (such as dead carcasses or bones) is a bad sign.  The water there may be highly polluted (by man or nature) and should be avoided.  Desert lakes without outlets can become salt lakes and must be distilled prior to drinking.

 

Ice and Snow

Freezing does not sterilize water and many organisms can be suspended in ice for extended periods without affecting their virility.  From the infection standpoint, melted snow is preferred over melted ice, since ice is more likely to have suspended bacteria in it.  That said, you unfortunately need more fuel to produce a quart (liter) of water from snow than from ice and therefore, most alpine trekkers prefer to melt ice for drinking water than snow. 

 

Pink snow should be avoided as it may have toxic algae in it. 

 

Yellow snow should be avoided for obvious reasons.

 


Water Treatment

There are several ways to treat water to make it safer to drink.

 

The major types of water treatment used by hikers, backpacker and travelers are filtration, heat, UV radiation and chemical treatment.

 

Water Filters

Ongerth JE, Johnson RL, Macdonald SC, Frost F, Stibbs HH. Back-country water treatment to prevent giardiasis. Am J Public Health. 1989 Dec;79(12):1633-7.

 

This figure shows the effectiveness of several different filters at removing G. Lamblia cysts.  Note that all filters are not created equal.  The Pocket Purifier (Calco Ltd) had literally no effect on removing G. Lamblia cysts in water while the 1st Need and Katadyn ones did a remarkable job at removing all detectable cysts.  Note that most filters have no effect on viruses which may be in your water.  See filtration below.

 

 

Heat Water Treatment

Ongerth JE, Johnson RL, Macdonald SC, Frost F, Stibbs HH. Back-country water treatment to prevent giardiasis. Am J Public Health. 1989 Dec;79(12):1633-7.

 

This figure shows the inactivation of G. Lamblia cysts after application of heat for 10 minutes.  The majority of G. Lamblia appears to drop off after water is heated to 50 degress C.  The sensitivity of other organisms to heat will vary.  The consensus is that 5 minutes at 65 degrees C will inactivate most harmful microorganisms (to include the hepatitis A virus).  See heat below.

 

 

UV Light Dose to Inactivate

Log Inactivation Cryptosporidium

UV dose (mJ/CM2)

Giardia lamblia

UV dose (mJ/CM2)

Virus

UV dose (mJ/CM2)

0.5 (68.4%) 1.6 1.5 39
1.0 (90%) 2.5 2.1 58
1.5 (96.8%) 3.9 3.0 79
2.0 (99.0%) 5.8 5.2 100
2.5 (99.7%) 8.5 7.7 121
3.0 (99.9%) 12 11 143
3.5 (99.96%) 15 15 163
4.0 (99.99%) 22 22 186

40 CFR 141.720  - INACTIVATION TOOLBOX COMPONENTS.  CFR-2011-title40-vol23-sec141-720.pdf

&

"National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface Water Treatment Rule". Federal Register (U.S. Environmental Protection Agency) 71 (3): 783. 05-Jan-2006. Retrieved 17-Apr-2010.  03-18295.pdf

 

This table shows the dose of UV light required to inactivate Cryptosporidium, Giardia lamblia and virus per the US EPA. Cryptosporidium and Giardia lamblia are far more susceptible to UV light than virus.  A chemical treatment in addition to UV light may be an acceptable treatment option for a backpacker if you are unable to produce the amount needed to sterilize you water with light alone. See UV radiation below.

 

 

Chemical Treatments

Ongerth JE, Johnson RL, Macdonald SC, Frost F, Stibbs HH. Back-country water treatment to prevent giardiasis. Am J Public Health. 1989 Dec;79(12):1633-7.

 

This figure shows the effectiveness of several different chemical treatments to G. Lamblia cysts.  The chlorine compounds were relatively infective while iodine was more so effective, especially after 8 hours of contact time.  Note that these chemicals will be more effective against bacterial and viral pathogens, but may need to be used in conjunction with a filter or UV light to removal or inactivate protozoal cysts.  See chemical treatment below.

 

 

For more information on various treatment options, there is an excellent commercial water treatment device database developed by the US Army Center for Health Promotion and Preventive Medicine available on the web.

 

 

US EPA Product Registration

Most water treatment products should be registered with the US EPA (Environmental Protection Agency) and have an EPA registration number if available for sale and use in the US.  Registration in no way means that the product has been approved as a purifier by the EPA or is effective in any way.  Advertisements or published articles stating EPA approval are more often than not misleading and should be disregarded.  Being "independently certified to meet EPA Microbiological Purification Standards" sounds great, but does not constitute EPA approval or effectiveness of any product or technique.  EPA registration simply means that it the EPA feels that it is safe to use, not that it is effective.

 

Often seen with the EPA registration number is the EPA Establishment Registration Number (EPA Est. No.).  This is simply the company number followed the the state abbreviation and then the Establishment Number of the last phase of pesticide production takes place.  Like the EPA registration number, this does that certify the the product in question is effective in any way.

 

Water Treatment Subcategories

Filtration

Organisms such and protozoa and bacteria can be filtered out of water in sufficient numbers with an appropriate filter system.  Filters can also do a great job of filtering out sediment and things that may cloud or taint the taste of water (algae, fecal particles, etc).  Commonly pathogenic bacteria can be as small as 0.2 microns, so filters able to filter out to 0.2 microns are preferred over those that can't.  For just filtering out protozoa, a 1 micron (μm) or less filter is recommended.  Mechanical filters may be able to filter out many of the particles that viruses are attached to but can not filter out viruses.

 

It is important to know that filter pore size can be rated in several different ways.  The most common methods of measuring pore size is by absolute size, nominal size and average size.

 

Absolute pore size is the size of the largest particle (such as a glass bead) that will pass through a filter membrane under a specific set of testing conditions.  This is used with filter membranes that have uniform cylindrical pores (capillary-pore membranes).  This may seem like the safest measuring system to use, but results can vary significantly based on testing techniques.  Some manufacturers may also choose to redefine their absolute pore size with a non absolute value, such as defining it as being able to remove 85% of particles of a given size.

 

Nominal pore size is the percentage of particles (such as glass beads) removed of a certain size.  An example would be 70% removal of 0.5 μm particles filtered.  This is used for sponge-like tortuous path filter membranes where interconnected  pore of various sizes creates a labyrinth.  Depth filtration works in conjunction with size exclusion.

 

Average pore size is just that - the average size of pores.  Many pores will be larger and many will be smaller.  This sizing system gives you a very rough estimate of filtering capabilities at best.

 

Of these three pore sizing systems, absolute pore size is generally the most accurate at quantifying true filtering.  As stated earlier, even absolute pore sizing can vary depending on testing technique and definition.

 

Filters do not work well against viruses (after initial publication of this page - Sawyer came out with a filter system which claims to filter out virus) and are not recommended for use in areas of high virus risk.  Also, the effort involved with pumping filters can quickly become a nuisance and may cause filter users to consume less water or take more chances at drinking unfiltered water.

 

Depending on construction, filters will also need to be maintained from time to time.  Filter elements will need to be replaced or cleaned as the filters become clogged and may need to be back filtered with clean water to unfoul the filter enough to prolong its usable life.  Replacement filter elements can be difficult to find while abroad and can cost almost as much as the original unit.

 

The advantage of filters is that they can often be used for extended periods without concerns of resupply (for ceramic filters), batteries or a chemical taste in their water.  They also filter out a lot of undesirable particles in water, making it look and taste more potable.

 

Filter and Purifier Types

 Katadyn Water Filter

Hand Pump Filters

Water filters that use a hand pump to force water through filters are the most common type of filter system for portable backpack filters.  They may require a little priming, but are pretty simple to use.

 

High quality units can be a bit bulky and surprisingly expensive.

 

 Katadyn Siphon Filter

Gravity Filters (Siphon Filters)

Gravity filters usually need to be hung from a tree or other appropriate high point so that the weight of water on top of the filter provides enough force to push water through it without the need for manual pumping.  Siphon filters work in a similar manner, using the gravity to pull water through a filter from a higher point to a lower point.  It may take a bit of time to filter a days worth of water in this manner, but requires little effort other than setup.  These setups are better suited for base camp use where there is no hurry to filter water.

 

 

 

These can also be homemade with a little ingenuity and commercial examples include the Ortlieb-Syphon Filter and Katadyn Syphon Filter.

 Katadyn Bottle Filter

Bottle Filters

There are several products that incorporate a filter into a water bottle.  They sound great in concept but generally are only capable of filtering out protozoa and large sediment at best.  These are generally not suitable for filtering out bacteria or viruses.

 Aquamira Straw Filter

Sippy Filters (Survival Straw)

A few filters are set up so that you can suck water through a filter.  These are ok for filtering small amounts of water.  Many of these have large pored filters that allow you to suck water through them without injuring yourself, but are only effective against protozoa at best.  Some of these have demonstrated no effective filtering against Giardia cysts.

 Reverse Osmosis Filter

Reverse Osmosis

These filters are designed to force water through a membrane that is impermeable to most contaminants.  It is often used to desalinate water and can be used to remove pathogens from water.  The membranes used for these devices are easily fouled and not designed for fresh water use.

 

The AquaPack Desalinator is an example of a man portable reverse osmosis filtration system powered by a 4 stroke engine.  This may be useful for NGOs and Marine units needing to desalinate moderate amounts of water.

 First Need Water Purifier

Purifiers

Purifiers are filters with a purifying feature such as chemicals or use of an electrostatic charge (First Need purifier) to kill or inactivate the viruses that the filter can't remover.  The idea of a filter/purifier combination sounds great in theory but may not work as well as advertised, especially in cold environments, where you may need to double filter or significantly slow filtering to allow enough contact time with the water and purifier element.

 Chlor-Floc Purification Tablets

Flocculating Agents

Flocculating agents allow for removal of suspended solids in water by promoting rapid clomping and sedimentation of fine particles suspended in water. This sediment is then easily removed by straining the water through a cloth or by siphoning or pouring off just the clear water. This isn't a "filter" treatment in itself but allows for the removal many suspended solids to improve clarity and taste of water as well as decreasing the amount of treatment (chemical/filtration/heat/radiation/etc) needed for your water. Flocculating and coagulation can remove 6098% of microorganisms, heavy metals, and some chemicals and minerals from water.

 

The US military uses Chlor-Floc water purification tablets which uses aluminum sulfate as a flocculating agent.

 

Alum (aluminum sulfate) has long been used as a flocculating agent.  Simply add a pinch of alum (1/8th teaspoon) to a gallon of water, occasionally stir it over 60 minutes and then leave to settle for 30 minutes.

 

Backpackers can use backing powder or fine white ash if needed.

 

Other flocculating agents include:

  • aluminium potassium sulfate (also referred to as alum) generally 10-30 mg/quart (liter)

  • aluminium chlorohydrate

  • aluminum sulfate

  • calcium oxide

  • Lime (calcium hydroxide)

  • iron(III) chloride

  • iron(II) sulfate

  • sodium aluminate

  • sodium silicate

  • Chitosan

  • Moringa oleifera seeds

  • Papain

  • A species of Strychnos (seeds)

  • Isinglass

  • White ash

  • Baking powder

 

Sedimentation

If time is not a concern, water can be left to sit for several hours to allow solids to settle.  This can separate a lot of suspended matter in water and allows you to siphon or pour off the clear water on top.  This decreases the amount of further treatment needed for your water.  Giardia cysts sink in water and sedimentation should decrease the amount of Giardia in water.

 

You should allow at least 1 hour for sedimentation of most suspended particles and much longer for cysts.

 

Prefiltering

Prefiltering with a cloth or coffee filter doesn't safely remove enough microorganisms on its own to justify use as a sole water treatment in itself, but does remove many of the larger particles in water.  This removal of larger particles from water does have an impact on amount of microorganisms in water but it more importantly makes water more palatable and makes water easier to treat with chemicals or UV light and decreases the frequency of clogging of water filters.

 

Filter Membrane Construction

There are several different materials and designs used to create filter membranes.  The materials used, construction and quality of the membrane will determine the potential of what can be effectively filtered as well as its susceptibility to clogging and aspects of maintenance.

 

Membrane Microfilter

This design uses a membrane made from a thin layer of semi-permeable material.  These can include microfilters, ultrafilters, nanofilters, and osmotic membranes.

 

Depending on pore size, they can be effective in filtering bacteria and cysts.

 

Depending on the membrane configuration, microfilters can be susceptible to fouling from particulate matter and are difficult to clean and maintain.

 

Ceramic Microfilter

Ceramic microfilters are made from inorganic ceramic pastes derived from powdered alumina (Al2O3), zirconia (ZrO2), and titanium (TiO2).  This material uses symmetric pores in a tortuous path depth filtration structure.  Pores can be as small as 0.1 μm.

 

Depending on pore size, they can be effective in filtering out bacteria and cysts.

 

Ceramic allows for surface scraping of the filter after fouling to restore lost function.  This feature allows for extended use of a filter element and field maintenance when needed.  Some of these filters also have silver impregnated in them to decrease growth of pathogens in the filter itself.  The silver in these filters do little to disinfect contaminated water and are only suitable for decreasing colonization within the element itself.

 

Fiber and Fabric Filters

These filters can be made of compressed or cast fibers such as cellulose papers, woven fabrics, and glass (such as borosilicate glass).  Pores can be as small as 0.2 μm.

 

Depending on pore size, they can be effective in filtering bacteria and cysts.

 

Some Fiber filters allow for cleaning while others are non-cleanable.  Non-cleanable filters, require replacement once clogged.

 

Granular/Powdered Carbon

Granular activated carbon (GAC) and powdered activated carbon (PAC) are often made from coconut shells, peat, lignite, coal or wood.  These are used for the sole purpose of reducing taste and odor of water.  These are often used to remove chlorine taste from tap water.  They are also good for removing iodine taste from iodine treated water.

 

Alone, it is not suitable for treating microorganisms. 

 

Carbon Block

Carbon blocks are heat molded from powdered carbon, thermoplastic binders, and other additives.  They can filter out considerably much more than loose carbon, but also have slower flow rates.  During manufacturing, these can be impregnated with silver of chloramine to hinder or prevent bacterial growth within the filter.

 

May be effective against protozoan cysts but pore sizes are too large to effectively reduce bacteria counts.

 

Like other filters, prefiltering is necessary to prevent fouling.

 

Ion Exchange

Usually uses resin beads 0.04 to 1.0 mm in diameter and made of polystyrene divinylbenzen or other materials.  As the name implies, ions in the resin are exchanged for ions in the water.  This is generally used for water softening and removal of heavy metals.  Resins can often be recharged to some degree.

 

Iodine ions may be effective against some microorganisms through disinfection, whereas other types of ion exchange systems are not effective against pathogens.

 

Like other filters, prefiltering is necessary to prevent fouling.

 

Osmosis

This system uses osmotic semipermeable membranes to separate water passively.  It tends to be extremely slow but isn't effected by water turbidity and doesn't develop caking of sediment and fouling of the membranes.

 

Can be effective at reducing bacteria, viruses, and cysts.

 

This system is passive and therefore eliminates the fouling effects of turbid water.  So unlike most other systems, prefiltering is not required.  Filter is also very slow and negatively impacted by cold temperatures.

 

Reverse Osmosis

This type of filtering system requires a semipermeable membrane that allows water to pass through it but not solutes.  Pressurizing of the influent side is necessary and there is some debate as to whether the membranes used are non-porous or have selective pores.

 

Can be effective at reducing bacteria, viruses, and cysts.

 

These are not designed for fresh water treatment and are very prone to filter fouling.  Effective prefiltering is necessary to prevent fouling and this is not a feasible system for microbial or particulate reduction of fresh water.  They can be ideal for sea survival since they are designed for desalination of sea water.

 

Boiling and Pasteurization

The right amount of heat does a good job of rendering pretty much all harmful organisms that may be present in water ineffective.  Depending on the temperature and duration of heat applied to water, it can be either sterilized or pasteurized to make it safe to consume.  Sterilization of water involves boiling water to the point that all organisms in it are dead.  Pasteurization involves heating it to the point that all harmful microorganisms are killed or inactivated.

 

The disadvantage of using heat to treat water is the need for fuel, cooking gear, and time needed to set up, heat and cool.  It also does not remove sediment from your water.

 

Alcohol Stove

 

Sterilization

In order to sterilize water, and render all organisms ineffective, you will need to boil your water for a minute or so (varies between recommendations and altitude).  Some recommendations include boiling water for 5, 10 or even 20 minutes to eliminate all bacterial spores that may be present in water.  This unfortunately requires a significant amount of fuel, which can become a major consideration when in the outback (unless local wood, electricity, solar power or fuel sources are options).  Heating water to this extent is also unnecessary, unless you need this water for surgery.

 

Pasteurization

Luckily, not all of the organisms found in water are harmful when ingested.  Significantly less heat is needed to inactivate harmful microbes than is necessary to bring water to a boil.  Inactivation of these microbes actually starts as low as 5C (9F) but requires a significant amount of time to kill harmful pathogens.  The consensus is that regular pasteurization requires heating of water to 65C (149F) for 5 minutes to kill 99.99% of harmful organisms, to include Giardia, cryptosporidium, endameba, the eggs of worms, cholera, enterotoxogenic strains of E. Coli, salmonella, causative organisms for typhoid, shigella, Hepatitis A, and rotavirus.  This doesn't require as much fuel as sterilization, but requires a thermometer, heat gauge or test kit.

 

Temperature where 90% of organisms are neutralized per minute

Microbe Temerature
Worms, Protozoa cysts (Giardia, Cryptosporidium, Entamoeba) 55C (131F)
Bacteria (V. cholerae, E. coli, Shigella, Salmonella typhi), Rotavirus 60C (140F)
Hepatitis A virus 65C (149F)

 

A safe and simple rule recommended by the WHO is to simply bring water to a rolling boil.  This will heat it up sufficiently to kill any harmful microorganisms that may be present in your water and is an easy way to gauge whether or not your water was hot enough to be effective.

 Water Distiller

Distillation

This involves collecting water vapor so that many pathogens and contaminates are removed.  This is a common method for separating drinking water from minerals or salts.

 

Besides electric home systems, there are several ways to make a field distiller.  Field systems such as solar distillers can be difficult to construct and may be extremely slow at producing drinkable water.

 

UV Radiation

UV radiation works by damaging the DNA in microorganisms.  It has long been used in commercial and municipal water treatment and is sometimes used to sterilize operating rooms and surgical equipment.  The susceptibility to UV radiation varies greatly between various pathogens and protozoan cysts tend to be very resistant to UV radiation.

 

References:

USEPA, Ultraviolet Disinfection Guidance Manual for the final LT2ESWTR, Nov 2006 guide_lt2_uvguidance.pdf

Require 3-Log (99.9%) inactivation of Cryptosporidium and Giardia and 4-Log  (99.99%) inactivation of Virus

40 CFR 141.720  - INACTIVATION TOOLBOX COMPONENTS.  CFR-2011-title40-vol23-sec141-720.pdf

3-Log inactivation of Cryptosporidium and Giardia require UV dose of just 12 mJ/cm sq.

4-Log inactivation of Virus requires 186 mJ/cm sq.

 

"National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface Water Treatment Rule". Federal Register (U.S. Environmental Protection Agency) 71 (3): 783. 05-Jan-2006. Retrieved 17-Apr-2010.  03-18295.pdf

3-Log inactivation of Cryptosporidium and Giardia require UV dose of just 12 mJ/cm sq.

4-Log inactivation of Virus requires 186 mJ/cm sq.

 

Mofidi, AA; Meyer EA, Wallis PM, Chou CL, Meyer BP, Ramalinham S, Coffey BM (2002-Apr). "The effect of UV light on the inactivation of Giardia lamblia and Giardia muris cysts as determined by animal infectivity assay". Water Research 36 (8).  PubMed  12092585

G. lamblia and G. muris cysts showed >2-log10 (99%) sensitivity to 3 mJ/cm sq UV light

 

Campbell, Andrew; Wallis, Peter (2002-Feb). "The effect of UV irradiation on human-derived Giardia lamblia cysts". Water Research 36 (4): 963969. doi:10.1016/S0043-1354(01)00309-8.  PubMed  11848367

UV dose 254 nm resulted in significant inactivation of the Giardia cysts.

UV dose ~ 10 mJ/cm sq resulted in up to 2 log (99%) inactivation
UV dose 40 mJ/cm sq resulted in up to 3 log (99.9%) inactivation

 

Qiu X, Sundin GW, Chai B, Tiedje JM (November 2004). "Survival of Shewanella oneidensis MR-1 after UV Radiation Exposure". Applied and Environmental Microbiology 70 (11): 643543. doi:10.1128/AEM.70.11.6435-6443.2004. PMC 525172.  PubMed  15528503

Organisms inactivated by UV light can undergo photoreactivation after exposure to visible light

 

Linden, KG; Shin GA, Faubert G, Cairns W, Sobsey MD (2002-06-01). "UV disinfection of Giardia lamblia cysts in water". Environmental Science and Technology 36 (11).  PubMed  12075814

Reduction of G. lamblia infectivity for gerbils was very rapid and extensive, reaching a detection limit of >4 log within a dose of 10 mJ/cm sq

no evidence of DNA repair leading to infectivity reactivation following typical drinking water and wastewater doses of 160 and 400 10 mJ/cm sq

 

A & L Laboratory, Auburn Maine 5/21/2008: SteriPEN meets the requirements of NSF International P248 Protocol for Emergency Military Operations Microbiological Water Purifiers for 3 Liter Hydration Bladders.  a_lbladderp248revised9408.pdf

Company sponsored study demonstrated: SteriPEN delivered UV doses in excess of the required 40mJ/sq cm

 

 

Small portable units are available to backpackers and claim to be effective against  protozoa such as Giardia and cryptosporidium as well as against bacteria and viruses.

 

Small portable units may need a good supply of batteries or rechargeable batteries and a charger (manual, solar, car or 110/220V) for longer travels.  This can really add to the bulk, weight and complexity of this option of water treatment.

 

Also see US EPA UV Water Treatment.

 

 

 

  AquaStar

AquaStar

AquaStar claims to be effective against protozoa (Giardia, Entamoebic Dysentery, and Cryptosporidium), bacteria (Cholera, Shigella, Salmonella, and E. coli) and  viruses (Enterovirus, Rotavirus, Hepatitis, and Poliovirus) with a dosage time of 80 minutes per quart (liter).  It is supplied with a Nalgene bottle for protecting the unit as well as providing a container for water treatment.

 

AquaStar also has a 2.4oz mV floating bobber UV water purifier.  It has an internal rechargeable lithium battery that can be recharged with just about any commercial battery via magnetic electrodes.

 SteriPEN

SteriPEN

SteriPEN claims to be effective against bacteria, viruses and protozoa.  They have multiple compact and portable units for backpacker use. 

 

Other Portable UV Systems

First Water Systems (Aqua Sun), Aspen Water and Noah Water Systems market portable high volume water purification systems.  These may be good options of small groups, NGOs or remote outpost use.

 

Solar Photooxidative Disinfection (Sol-Air Water Treatment, SODIS)

This technique uses sunlight to convert trapped oxygen in water into hydrogen peroxide and oxygen free radicals.  A combination of these free radicals and heating of the water from the sun is more effective than either alone. Laboratory testing has demonstrated a thousand fold reduction in fecal coliforms with exposure to 4.5 hours of bright sunlight. Obviously, this system of water treatment is highly dependant on many factors such as sun position and intensity, weather, and time to treat.

 

You need bright sunlight, a clear uncolored water bottle (preferably painted black on one side) and a lot of time for this treatment method.  Glass bottles work fine and PET (polyethlyene terephtalate) plastic bottles are preferred over those made of polyvinylchloride (PVC) since there is less of a concern of leaching of plasticizers into your water.

 

Turbid water should be allowed to settle or filtered first to remove suspended matter in your water.  Then, fill 75% of your 1-2 liter bottles with water (ideally greater than 50C or 122F) and give it a good shake for a couple of minutes and leave in the sun (preferably in the morning).  You should reshake your bottle every couple of hours or so to mix oxygen with your water.  At the end of your day, your bottle should be reasonably free of bacteria.WAPI

 

Your target range of water treatment is between 50C (122F) and 65C (149F) with 55C (131F) being ideal.  If plan on this form of water purification, it would be ideal to use a reusable water pasteurization indicator (WAPI).  This is generally made from a weighted plastic tube with a plug of wax (Myverol 18-06 K) in it.  When the proper temperature is achieved, the wax melts and falls to the bottom of the tube, indicating proper levels of heat for pasteurization (see image of before and after).  After use, you can flip the WAPI upside-down like an hourglass and reuse it.

 

If supplies are available, a solar stove may be more efficient and water can be truly pasteurized in a shorter amount of time.

 

Chemicals

Chemicals such as chlorine and iodine have long been used against bacteria and viruses.  They are generally inexpensive, very packable, light and overall quite backpacker friendly.  Unfortunately, many of the commonly used chemicals lack effectiveness against hard shelled protozoan cysts such as cryptosporidia.

 

The effectiveness of all water treatment chemicals depend on the concentration of the chemical, temperature of water, the contact time with the water and murkiness of the water itself.  The following rules apply to most water treatment chemicals:

 

  1. Most chemicals used for water treatment are reactive and most are "used up" or age over time.  The older a chemical is or the longer it is exposed to air, the less likely it will be effective.

  2. Using inadequate concentrations of chemicals (due to age of chemical, accidental under dosing, or desire for better taste) will increase the time needed to treat your water or lack enough chemical to neutralize all organisms in your water.  Half doses of chemical generally need twice the treatment time.

  3. Decreased water temperatures (common in mountains) will require more contact time or higher concentration levels to be effective. 

  4. All chemicals require a certain amount of time for it to work.  If you consume water before the chemicals added to it have a chance of neutralizing the pathogens in it, you are little better off than drinking untreated water. 

  5. Sediment in water will necessitate the need for more chemical as murky water is likely to have more pathogens and the sediment itself will consume or bind to some of the chemicals.  The going rule is to use twice as much chemical for cloudy water than you would use for clear water.  Very turbid water may need to be prefiltered (with filter, clean sock, etc) or allowed to settle prior to treatment.  And when using a filter in conjunction with chemicals, you should use the chemicals after filtering as the chemicals will be more effective.

  6. Taste after treatment.  You need to allow chemicals to thoroughly treat your water prior to adding any taste neutralizing chemicals or drink mix.  Left over neutralizers and drink residue in a water container will neutralize some of chemicals if not washed out prior to your next treatment.

 

When used in conjunction with a good quality water filter, you should be able to safely treat water from all harmful microorganisms as well as have some residual protection from the remaining chemicals in the water.

 

The downside of chemical treatment include the chemical aftertaste as well as the need to wait for the chemical to do its job.  Cold water requires longer wait periods to be effective.

 

To assure treatment of all questionable water with chemicals, make sure you treat the water trapped in tubes or the thread of your water container.  To achieve this, add the appropriate amount of your chemicals, shake your container, wait at least thirty seconds, then loosen the cap of your water container and allow some fluid to leak out.  If you have a water nozzle (such as in a Camelback), allow some of the newly treated water to leak out.  This allows treatment of all potentially contaminated water that may come in contact with your mouth.

 

Chlorine Dioxide (ClO2, Micropur MP1, Potable Aqua, AquaMira, Pristine, KlearWater)

Chlorine Dioxide is actually not a chlorine purifier.  It works very differently than chlorine and does not share many of the limitations that chlorine has.  Chlorine dioxide is a powerful oxidant that has excellent germicidal properties that kills microorganisms by disrupting transport of nutrients across the cell wall.  It is also unaffected by pH in the range normally encountered in water treatment.

 

It also does not discolor water, is tasteless and may be the chemical treatment of choice for many backpackers since it is very portable and effective against protozoa, bacteria and viruses.

 

Many chlorine dioxide purifier products are actually "stabilized chlorine dioxide" (SCD). These products usually contain solutions of buffered sodium chlorite that are activated with a weak acid to make chlorine dioxide.

 

2NaClO2 + 2HCl + NaOCl → 2ClO2 + 3NaCl + H2O

or

5NaClO2 + 4HCl → 5NaCl + 4ClO2

 

Also see US EPA Chlorine Dioxide Water Treatment.

 

Chlorine Dioxide via Sodium Chlorite and Sodium Bisulfite Tablets

Katadyn's Micropur MP-1 Water Purification Tablets is a popular stabilized form of chlorine dioxide purifier and has been approved by the EPA as a "purifier".  Manufactured in Spain, tablets are made up of 6.4% sodium chlorite and 1.0% sodium dichloroisocyanurate dihydrate.  Chlorine dioxide is formed in this system by a reaction of sodium chlorite (NaClO2) with sodium bisulfite (NaHSO3) and chlorine from sodium dichloroisocyanurate dihydrate.  Katadyn claims this product is effective against Giardia and Cryptosporidium if water is treated between 30 minutes (20C and clear) and 4 hours (4C and dirty).

 

Katadyn Micropur MP1 Purification Tablets
Microorganisms Killed Contact Time Requied Contact Time Requied
  EPA Water Test #1
(clear, 20C or 68F)
EPA Water Test #2
(very dirty, 4C 38F)
Bacteria 15 Minutes 15 Minutes
Virus 15 Minutes 15 Minutes
Cysts 30 Minutes 4 Hours

 

Potable Aqua has a chlorine dioxide treatment product that appears to have the identical active ingredients of Micropur MP-1 and is also manufactured in Spain.  Other companies make similar chlorine dioxide tablets or preparations but don't have EPA approval for various reasons, possibly due to lower concentrations of chemical or the lack of interest and effort in getting EPA approval.

 AquaMira Chlorine Dioxide

Chlorine Dioxide via Sodium Chlorite and Phosphoric Acid Solutions

AquaMira uses a stabilized 2 part liquid system for chlorine dioxide.  Part A contains a 2% sodium chlorite solution and Part B contains 5% phosphoric acid solution.  Seven drops of each are mixed and added to a quart (liter) of water.  You will need wait several minutes for the two components to react prior to adding it to your water.

 

This two part liquid form chlorine dioxide is EPA registered, which is different than being approved as a purifier.

 

 

Chlorine Dioxide in Stabilized Liquid Form

KlearWater has a 0.15% activated liquid chlorine dioxide in deionized water packaged in a portable glass bottle.  The advantage of this system is that it doesn't require a mixing and a reaction time prior to adding it to your water.  The solution itself can also be used as an antiseptic.

 

One ml of fluid is used to treat one quart (liter) of clear water and a measuring system is built into the cap.

 

This solution has an 8 month shelf life once opened and refrigerated and about half the self life is kept in a cool dark place.  The color of the solution should be yellow when you first use this product, which indicates when it is active.  When the yellow color is no longer noticeable, it's time for a new bottle or different treatment system.

 

Chlorine-Releasing Agents

Sodium hypochlorite and other chlorine-releasing agents have long been used to treat water.  Under proper conditions, they kill bacteria and viruses and allows for residual protection when small amount remain after treatment.  Chlorine can also inactivate Giardia cysts to some extent but is less effective than iodine.  These agents should not be relied upon for treating hard shelled protozoa.  According to Back-country water treatment to prevent giardiasis. (Ongerth, et al. American Journal of Public Health December 1989, Vol 79, No 12, pp 1633-1637.), chlorine is relatively ineffective against giardiasis even after 8 hours of use.

 

The WHO standard for chlorine treated water is a final residual chlorine level of 0.2 to 0.5 mg/l after a 30 minutes of contact time. This may require as much as 5 mg/L of chlorine.  Others feel that a dose of 8mg/L is better suited for field use. 

 

The best way to determine treatment by chlorine is to measure residual levels of chlorine and multiply it by the minutes of exposure to determine its CT value (min mg/l).  Since most backpackers are not going to have a chlorine test kit readily available on most of their journeys, a field rule is to make sure there is a slight chlorine smell after treatment with chlorine.  If there isn't a chlorine smell after treatment, you may need to retreat your water.

 

Cryptosporidium is highly resistant to chlorine and inactivation requires exposure to 80 mg/L of free chlorine for 120 minutes in clear water.  The CT values needed to treat for Giardia can be quite high (500+) depending on pH and temperature of water and are usually not reliably inactivated by doses and treatment times used by backpackers.  You should therefore not depend on chlorine alone to treat Giardia, Crypto or other protozoa.

 

Chlorine unfortunately has a number of drawbacks as a water purifier.  For one, chlorine ions attached themselves to organic material (nitrogen containing compounds such as amino acids) and is "used up" in cloudy or heavily contaminated water, leaving less free chlorine available for disinfection.  So unless you are testing for chlorine levels after treatment, you will need to use higher levels of chlorine to ensure proper treatment of water.  It may also be necessary to prefilter water to remove organic material and allow for lower doses of chlorine, filter water after treatment with a charcoal filter, or use peroxide or other chemicals to remove chlorine after treatment to avoid the chlorine "swimming pool" taste than many find so offensive. 

 

There is also a concern of carcinogenic trihalomethanes that are produced from chlorine treated water.  These are created when chlorine ions bind to organic debris in water.  Yuck.

 

In water, chlorine-releasing agents release hypochlorite ions (OCl-) which establish an equilibrium with hypochlorous acid (HOCl).  The equilibrium between hypochlorite ions and hypochlorous acid is highly pH sensitive.  At lower pHs (between 4 and 7), hypochlorous acid predominates, but at higher pHs (above 9), chlorine tends to mostly dissociate into hydrogen and hypochlorite ions.  This is an important characteristic of chlorine-releasing agents since hypochlorous acid seems to be better suited at penetration of outer cell layers of microorganisms.  It forms chlorinated derivatives of nucleotide bases and disrupts oxidative phosphorylation and other membrane-associated activity.  In comparison, the hypochlorite ions can't penetrate the cell wall of bacteria and viruses and have a minute effect against microorganisms compared to undissolved HOCl.  Because of this, chlorine-releasing agents become poor disinfectants at a pH of greater than 8.

 

Over time chlorine products turn into chlorine gas and loose their potency as the chlorine is slowly gassed off.  Agitation and exposure to air increases this chlorine loss, which makes it less than ideal for backpacking and long term storage.

 

Because of chlorine's instability when agitated or aged, its pH-sensitive limitations, propensity to be used up as it binds to organic material in water, its slow speed at disinfecting, and its inability at reasonably inactivating protozoa with acceptable levels of chlorine, it can't be trusted to treat protozoa and sometime viruses when used to disinfect small quantities of water.  For large quantities of water disinfection, chlorine treatment can't be beat given its low cost, simplicity and safeness of use.

 

These are 1% strength equivalences

70% Calcium hypochlorite crystals 14.3g/L
35% Calcium hypochlorite granules 28.6g/L
NsDCC (60% chlorine) 16.6g/L
Chloramine Tablets (1 gm chlorine) 40g/L (40 tabs/L)
NaDCC tablets (1.5 gm chlorine) 8 tabs/L
Liquid bleach (5.25%) 6.5 fl oz/L (191mL/L)

 

A liter of 1% strength solution has enough chlorine to treat 2,000 liters of water with 5 mg/L (PPM).

12 drops of 1% strength solution is enough to treat a quart (liter) of water to about 5 mg/L (PPM).

 

Also see US EPA Chlorine Water Treatment.

 Bleach

Bleach (NaOCl, Sodium Hypochlorite, ViralStop, Drinkwell Chlorine)

Regular chlorine bleach (without additives, soaps, fragrances, etc) can be stored in a properly relabeled eye dropper bottle for easy packing and use.  It is cheap, easy to find and makes a great contingency water purification option in times of natural disasters or when other disinfection options (such as boiling water) are not available.

 

Unfortunately, chlorine is lost when bleach is agitated, which is more or less unavoidable for backpackers.  Since it is difficult to determine how much chorine is left remaining after several days of trekking and transport, unused bleach should be replaced with fresh bleach when possible and practical.

 

When using bleach, make a not of the concentration being used.  Depending on brand and what part of the world you are in, concentration can range from 2-15% sodium hypochlorite.

 

Simply use 2 drops of (6% sodium hypochlorite) per quart (liter) for clear water and 4 drops per quart (liter) for murky water.

 

ViralStop is 3.5% sodium hypochlorite and is designed to be used with the Guardian Purifier System to treat bacteria and viruses.  It is basically half strength bleach.

 

Bleach can be used for larger scale water disinfection.  You can roughly use 1/8 teaspoon (approximately 0.75 milliliter) of 5.25% chlorine bleach per gallon of water or use the following chart for large amounts.

 

5mg/L (PPM) concentrations with

Laundry Bleach (5.25% Chlorine)

Liters Gallons mL fl oz
250 66 24 0.9
500 132 48 1.7
1000 264 96 3.3
2000 528 191 6.5
3000 792 286 9.7
5000 1320 477 16.2
10,000 2641 953 32

 Halazone Tablets

Halazone tablets (C7H5Cl2NO4S, 4-(Dichlorosulphamoyl) benzoic acid, Pantocid.)

These are relatively inexpensive ad have been used since World War II.  These tablets require crushing and shaking to mix in your water.  Once the tablets contact water, chlorine is release into it.

 

Because of questions of efficacy, Halazone was pulled from the US market by its manufacturer.

 

Earlier Halazone dosing recommended 2 tabs per quart (liter), but 6 tablets per quart (liter) and 1 hour of contact time is more likely needed to adequately treat water under most conditions.

 

A dosing of 5 tablets per quart gives you a concentrations of 7.5mg/liter.

 

Sodium dichloroisocyanurate (C3HCl2N3O3Na, Aquatabs, Micropur Forte, Chlor-Floc, NaDCC, Lifesystems Chlorine Tablets)

Sodium dichloroisocyanurate allows for a "reservoir" of chlorine which allows for a lower pH and higher proportions/levels of hypochlorous acid (HOCl).  Because HOCl is electrically natural and is similar in structure to HOH, it is more able to diffuse through the cell wall of bacteria than OCl- and in turn is far more damaging.  After diffusion through the cell wall by HOCl, chlorination (oxidation) of cell proteins or enzyme systems causes hydrolysis of peptidic chains of cellular membranes.  This makes this form of chlorine decontamination in many ways much more potent for water treatment than other chlorine treatment chemicals.

 

Aquatabs are usually dosed at one tab per quart (liter) to provide 5mg/L.  Thirty minutes of treatment time is required for bacteria and viruses and at least 90 minutes (450 mg min/L) of contact time is required to adequately treat for Giardia.

 

Superchlorination-dechlorination (The Sanitizer aka Sierra Water Purifier, shock chlorination)
This is a popular and effective two-step method of disinfecting with high levels of sodium or calcium hypochlorite (anywhere between 3-5 or 5-10 or 200ppm depending on guidelines used) and then neutralizing excess chlorine with peroxide or other reducing agents.  So much chlorine is used with this technique that the losses from high pH and organic binding of chlorine become insignificant.  It is quite effective and without the chlorine aftertaste once neutralized.  The end product should actually leave a signature sparkling taste.  Both chemicals needed for this process are highly reactive and can damage clothing and gear if spilled.

 

The Sierra Water Purifier called for 100 crystals (50 mg) of calcium hypochlorite (Ca(OCl)2 ) per gallon of water to superchlorinate it.  After superchlorination and sufficient time for sanitation, you add 6 drops of hydrogen peroxide (H2O2) to neutralize the remaining chlorine.  This produced a 11.5 mg/liter concentration.

 

Another example (also for Sierra Water Purifier) calls for use of 27 grams of calcium hypochlorite crystals per gallon of water which reportidly produces 27-30 ppm of free chlorine.  This is technique is described in several mountaineering medical manuals to include Medicine: For Mountaineering & Other Wilderness Activities 4th Edition.  A visitor pointed out that 27 grams of 70% calcium hypochlorite would create around 5,000 ppm of calcium hypochlorite, which would result in about 2,500 ppm of chlorine in water, which is well above the highest guideline (2,000ppm) recommended.  This 27 gram per gallon recommendation may be a misprint but would certainly sanitize your water.  If you instead add 27 milligrams of 70% calcium hypochlorite crystals to a gallon or 5mg per liter of water.  This yields around 2.5 ppm of free chlorine (which below the 3-5 or 5-10ppm recommendations for superchlorination).

 

1 Gallon = 3.785mL

27mg / 3.785mL = 7.1mg/L

7.1mg/L x 70% calcium hypochlorite = 5mg/L

5mg/L = 5ppm calcium hypochlorite

About 50% of the calcium hypochlorite is chlorine so -

If you just count just the mass of chlorine in solution, this comes out to about 2.5 ppm of chorine

 

After superchlorination, the recommendation is to wait 10 to 30 minutes (depending on temperature) and then add six drops of concentrated 30% hydrogen peroxide to dechlorinate the water.  The chemical reaction produces calcium chloride, water, and oxygen.

 

This technique is better suited for disinfecting large quantities of water than it is for disinfecting small amount of water needed for backpacker use.

 

Acceptable reducing agents include hydrogen peroxide, sodium sulfite, sodium bisulfite, and sodium thiosulfate.  Charcoal filters can also be used to remove excess chlorine.

 Calcium hypochlorite

Calcium hypochlorite (Ca(OCl)2, HTH, High Test Hypochlorite, Sentry, Perchloron, chlorinated lime, bleaching powder)

This is usually available in granular format or as non-effervescent tablets.  This is often used by military and aid agencies for large scale water treatment.  The US military uses ampoules to ease measurement of chemical needed to treat water trailers, Lyster bags, etc.  It unfortunately leaves a chalk residue that can cloud treated water and gives it a chalky taste on top of the chlorine taste.

 

Bleaching powder often comes in 33-37% strength and High Test Hypochlorite (HTH) comes in crystal form and has nearly 70% available chlorine.

 

Either a chlorination test kit is needed to titrate treatment or water can be intentionally over treated and then neutralized with a reducer.

 

One way to treat clear water is to first make a 1% solution of calcium hypochlorite by mixing 14 gram (one heaping tablespoon of granules) of HTH per quart (liter) of water.  Then adding 11 drops of this 1% solution can to each quart (liter) of clear water.  This produce about 5PPM chlorine, which is equivalent to 5 parts of 1% solution to 10,000 parts clear water.

 

5mg/L (PPM) concentrations with

Hypochlorite Granules (70% Chlorine)

Liters Gallons Grams
250 66 1.4
500 132 3.6
1000 264 7.1
2000 528 14.3
3000 792 21.4
5000 1320 35.7
10,000 2641 71.4
 

28.3 grams = 2 heaping tablespoons of granules = 1 once

 

Please note that HTH is highly reactive and can burn or explode if it comes in contact with reducing agents such as sodium thiosulfate, other chlorinating compounds, concentrated acids, and organic compounds such as antifreeze, oil, kerosene and gasoline.  You should never mix HTH with bleach.

 

Supertropical Bleach is composed of around 93% calcium hypochlorite and 7% of a strong base such as sodium hydroxide or calcium oxide (which changes into calcium hydroxide in water).  It is easier to spread and more stable for long term storage than HTH.  This type of powdered chlorine is used for chemical and biological decontamination and not for water purification.

 

Also see US EPA Sodium and Calcium Hypochlorite Salts Facts.

 Chloramine

Chloramine (NH2Cl)

Chloramine is made for the combination of ammonia and chlorine and has several advantages over chlorine when used in large water treatment facilities.  For one, fewer organic compounds (trihalomethanes) and other possibly carcinogenic byproducts (halogenic acetic acid) are formed when chloramine is used in lieu of chlorine.  Chloramines also remain in the water longer than chlorine and are more effective at higher pH.  The disadvantage of chloramine compared to chlorine is that it is slower acting and poorly effective against viruses and protozoa.

Tablets usually contain around 12-14mg of chloramine and require crushing and shaking to mix in your water.  This chemical also requires hours of contact time to be effective and is not recommended for backpacking water treatment for multiple reasons.

 

Also see US EPA Chloramine Water Treatment.

 Chlor-Floc

Chlor-Floc water purification tablets

Used by the US military, this system allows for sedimentation of suspended solids in water as well as treatment of bacteria, viruses and Giardia when used as directed.  It is not effective against Crypto.

 

Chlor-Floc uses sodium dichloroisocyanurate as a disinfectant and aluminum sulfate as a flocculating Agent.

 

AquaCure is another South African chlorine/alum purification tablet.

 Sodium thiosulphate

Sodium thiosulphate (Na2S2O3)

Sodium thiosulphate is used to lower chlorine levels following super chlorination.  Micropur Antichlorine contains sodium thiosulphate for use as a chlorine taste remover after water treatment is complete.

 

Sodium thiosulphate is also effective at nuetralizine free iodine into tasteless and microbiologically ineffective sodium iodide.

 

Iodine

Iodine is a chemical treatment alternative to chlorine and is considered more reliable than chlorine for highly polluted water and what travelers may encounter.  Compared to chlorine, it works faster, is effective over a wider range of pH, resists inactivation by organic matter and comes in several more stable preparations.  It is also relatively easy to use and many prefer the iodine taste over chlorine taste. 

 

It isn't completely clear exactly how iodine works against microorganisms but is seems to be able to rapidly penetrate them and attack key protein groups (cystein and methionine), nucleotides, and fatty acids which leads to the death of the organism.  In viruses, it may attack the surface proteins of enveloped viruses and destabilize membrane fatty acids.

 

Iodine can treat bacteria and viruses in low doses (0.5 mg/L).  Much higher doses (240 - 720 mg min/L) are required to treat Giardia and some studies suggest that greater than 24 hours of contact time may be needed to obtain a greater than 90% decrease in cyst load.  Other studies suggest a double dosage (16mg/L) of iodine and contact time of greater than 60 minutes is required to treat Giardia.  But literature supports a concentration of around 8mg/L as desirable for inactivation of Giardia cysts.  Iodine is not reasonably effective against Cryptosporidium and requires very high doses (1,015 mg min/L) in laboratory conditions to treat 99% of crypto in water.

 

Doubling of contact time or concentration (to 16mg/L) of iodine is usually recommended for treating cold or murky water.

 

An iodine residual of 0.5 to 1.0 mg/l should be maintained after iodine treatment if continued protection against pathogens is desired.

 

If the mediciny metallic aftertaste of iodine is an issue, it can be neutralized with a small amount (about 50mg) of vitamin C after treatment is complete.  It is important to note that small amounts of vitamin C remaining in water containers prior to treatment can neutralize iodine before it has a chance to disinfect your water.  An equal weight of sodium thiosulphate can also be used to convert free iodine to microbiologically ineffective and tasteless sodium iodide.  Charcoal filters can also be use to physically remove iodine from treated water.  Charcoal filter or add vitamin C, neutralizers and drink mixes only after treatment is complete and wash out containers prior to filling with untreated water.

 

Backpackers can also use half or quarter doses of iodine as long as they double or quadruple treatment times respectively.  This decreases the iodine aftertaste and conserves chemicals if treatment time is not a concern, such as when treating water prior to going to bed.  Decreasing treatment lower than 2mg/L will have little effect on taste.

 

Iodine comes in several different forms, mixtures and concentrations, but only free iodine and hypoiodous acid are capable of biocidal activity.  Since there are several iodine treatment options with varying concentrations of free iodine, dosing can be confusing.

 

Iodine Preparations

Preparation

Strength

Amount/Quart (Liter)

Iodine Tincture

2%

8 drops

Lugol's Solution

5%

4 drops

LifeSystems Iodine Drops

12%

3 drops

Povidone-Iodine

10%

4 drops

Tetraglycine hydroperiodide

8 mg

1 tablet

Iodine Crystal/water solution Saturated 13 ml
     
Titratable Iodine 1%  16 drops
Titratable Iodine 2%  8 drops
Titratable Iodine 3%  6 drops
Titratable Iodine 4-5%  4 drops
Titratable Iodine 6-7%  3drops
Titratable Iodine 8%  2drops
Titratable Iodine 16%  1drop

 

1 drop = 0.05 ml

 

Disinfecting Contact Times

Water Clarity

Water Temperature

5 C

15 C

Clear

30 min

15 min

Cloudy

60 min

30 min

 

Iodine appears safe for limited use, but there may be a concern if used continuously for greater than three months.  It can also present health concerns for those allergic to iodine or shellfish, pregnant women and folks with thyroid conditions if used for longer than 2 weeks.  Pregnant women who consume large amounts of iodine may have fetuses that develop goiters that can lead to respiratory obstruction at birth.  Several studies demonstrated no problems with long term iodine use except for persons with thyroid disorders.

 

Iodine is often labeled as highly poisonous, but it is difficult to overdose on iodine (unless you have significant allergies to iodine or thyroid problems) as it would take several grams to do the job and your body would probably vomit out a lethal dose prior to ingestion.

 

Concentrated Alcoholic Iodine (Polar Pure Plus)

You can mix 8 grams of iodine in 100cc of medical or food grade ethanol to yield an 8% iodine solution.

 

This formulation will not freeze and will not lose its strength over time.  In fact, as the alcohol evaporates, the solution becomes more concentrated.

 

Polar Pure has a concentrated iodine/alcohol mixture that is still pending EPA approval.

 

Two drops per quart (liter) gives you a concentration of 8mg/L and 100cc's of this solution is enough to treat 250 gallons.

 2% Tincture of Iodine

2% Tincture of Iodine

Topical iodine and tincture of iodine are the most readily available and cost effective iodine-based preparations for water purification.  Tincture of iodine is usually made up of about 1-5% iodine, 1-5% sodium iodide, 50% ethanol and water.  The sodium iodide is needed to dissolve the iodine, does little to purify water, and adds an unnecessary amount of iodine to your total intake of iodine when this is used for water treatment.

 

USP tincture of iodine should contain 2% iodine and 2.4% sodium iodide dissolved in 50% ethanol and water.

 

Iodine is sometimes formulated with methylated spirits which is not safe to drink.  You should only use USP or BP formulation of tincture of iodine, which are formulated with ethanol.  Iodine also needs to be stored in glass and not plastic to prevent leaching of iodine.

 

You will need 8 drops per quart (liter) of water.

 Lugol's Solution

5% Liquid Iodine (Lugol's Solution, Strong Iodine)

Strong iodine (5%) is often used for topically for farm animals and is available where farm supplies are sold.  Lugol's solution is made to be taken oral and is commonly used to wash and sanitize foods, treat food poisoning (6 drops in cup of water) and in various home remedies.

 

Keep in mind that Lugol's solution is sold in a wide range of strengths and the amount need to treat water will need to be adjusted accordingly.  With recent concerns of granular iodine being used to produce recreational drugs, lower concentrations of Lugol's solution are more commonly found in some places.

 

Lugol's solution of around 5% iodine, 10% potassium iodide and water will will require 4 drops per quart (liter) of water.

 

Lugol's solution of around 2% iodine will require 4 drops per quart (liter) of water.

 

Strong Iodine of around 7% (usually for veterinary use) will require about 3 drops per quart (liter) water.

 

Since these solution contain high levels of potassium iodide, you are consuming about 3 times as much iodine than if you were using iodine alone to treat water.

 

LifeSystems Iodine  (LifeSystems Iodine Drops)

There are a few formulations of concentrated iodine used for disinfection or for treatment of water.

 

LifeSystems Iodine Drops has 12% iodine and 12% potassium iodide.  The manufacture recommends 3 drops per quart (liter) and 6 drops if Giardia is suspected.  This is 2 to 4 times the conventional dose of 8mg/L but allows for consumption of water after a 3 minute wait, shaking and an additional 10 minute wait.

 Povidone-Iodine

Povidone-Iodine (C6H9I2NO, Betadine)

Iodine itself is poorly soluble in water and is usually dissolved in potassium iodide and ethanol to create an iodine tincture.  These tinctures and solutions with high concentrations of free  iodine can be very irritation to skin.  And when mixed with water, some of the free iodine will precipitate out of these tinctures.

 

Providone-iodine is a polyvinyl pyrrolidone-iodine water soluble complex that works as sustained-release reservoir of free iodine.  This enables providone-iodine solution to contain high levels of iodine without being too irritating to skin and without losing free iodine when mixed with water.

 

This disinfectant is often carried in first aid kits and because of its versatility as both a topical antiseptic and water purifier, it is the preferred chemical water treatment option by many backpackers, climbers and other outdoorsman.  But since it contains both povidone-iodine and free iodine, you are consuming conceivably more iodine than if you used just iodine alone to treat your water. 

 

The concentration of free iodine in providone-iodine solution is a complex matter.  Dilution of providone-iodine in water seems to weaken its hold on iodine, causing a release of free iodine into solution.  At full 10% strength, the concentration of free iodine is actually lower than when diluted down to 1:50 with water.   This increase in free iodine concentration begins to decrease somewhere around 1:50 dilution but concentrations differ amongst the various brands and formulations and is difficult to calculate.

 

Although providone-iodine is sold for water purification in some countries, this method lacks thorough testing and lacks proven efficacy.

 

Providone-iodine often comes in a 10% solution (1% titratable iodine equivalence).  Some recommend 8 drops per quart (liter) while others suggest about 4 drops per quart (liter) of water is needed to adequately treat water.

 

Tetraglycine hydroperiodide 16.7% (Globaline, Potable Aqua, Coghlans Drinking Water Tablets, EDWGT, TGHP, (NH2CH2COOH)4HI)

This is the most commonly used form of iodine used for water purification.  It comes in tablet form and those manufactured by Wisconsin Pharmacal (US military, Portable Aqua and Coghlan's) are made with tetraglycine hydroperiodide, sodium acid pyrophosphate (buffering agent) and talc (binding agent).  Iodine (I2) is produced when tetraglycine hydroperiodide reacts with water.

 

They are generally dosed one 8 mg tablet per quart (liter) of clear water and two 8 mg tablets per quart (liter) for cloudy or cold water.  For treatment of Giardia, you will need 16mgs per quart (liter) and at least 60 minutes of contact time.  These doses fall short of what is required to treat Cryptosporidium.

 

Brands such as Potable Aqua offers an optional bottle of neutralizing tablets (ascorbic acid) to decrease any after taste.

 

These tablets are said to have 6.68% titratable Iodine.  They should be steel gray in color and turn brown as they absorb water and lose their effectiveness.

 

One Coghlan's iodine tablet per quart of water gives you a concentration of 4.5 mg/liter.

 

One Portable Aqua tablet per quart of water gives you a concentration of 5.3mg/liter.

 

Iodine Crystals

USP-grade resublimed Iodine Crystals (Kahn-Vassher solution, Polar Pure)

This system incorporates a bottle of poorly soluble iodine crystals and is one of the best systems for treating small amounts of water, since it is relatively effective and has an indefinite shelf life.  This is probably the most reliable iodine treatment system available to backpackers and is widely used by mountaineers traveling abroad.

 

Glass is the only appropriate material for storing aqueous iodine solutions.  The main disadvantage of this is the potential of a full bottle freezing an breaking.  This can often be avoided by placing the bottle in your shirt, sleeping with it in your bag or only half filing it prior to nightfall.

 

Once water is added to your crystals, the water quickly (up to an hour) becomes saturated with iodine.  This saturated iodine solution is then added to your drinking water.

 

Since the amount of iodine saturated in water is dependant on the temperature of the solution, you should take into account the temperature of the solution to determine how much of it to add to the water you would like to treat.  The Polar Pure bottle and a thermometer on it for dose calculation for 4 mg/L.  The following chart shows how many capfuls (Polar Pure) of saturated solution are needed to treat water:

 

Temperature of Solution Capfuls per Quart (Liter)
95 F (35 C) 1.2
86 F (30 C) 1.3
77 F (25 C) 1.5
68 F (20 C) 2
59 F (15 C) 2.5
50 F (10 C) 3.5
41 F (5 C) 4

 

Saturation of iodine is increased if you keep the bottle warm by keeping it in your packet or setting it out in the sun prior to use.

 

For treating Giardia, it is recommended that you warm the bottle and use a double dose to 8mg/L for 90-120 minutes.

 

The original system system described by Kahn and Visscher in 1975 incorporates a 30cc (1 fl oz) bottle, paper lined bakelite cap, and 2-8 g USP grad resublimed iodine crystals.  The bottle is filled, shaken and left to stand for at least one hour.  At a temperature of 68F (20C), which can be maintained by placing the bottle in a shirt pocket, half a bottle (15cc) of saturated iodine solution should be able to treat one liter (quart) with about 9mg/L of iodine.  One 30cc (1 fl oz) bottle is enough to treat 2 liters of water.

 

Other guidelines recommend 13 ml (2.5 teaspoons) of saturated iodine solution pre quart (liter) of clear water or 25 ml (5 teaspoons) per quart (liter) of cloudy water.

 

It is important to note that the 4-8 grams of crystals used constitutes a potential lethal human dose if consumed all at once.  Because of this, the bottles supplied with Polar Pure are designed to trap the crystals when the iodine solution is poured out.  DIY backpackers should use a strainer insert in their bottles to prevent accidental pouring of crystals into your water.  These crystals can be purchased from a pharmacy.  Because of the poisoning potential, this system should not be entrusted with children.

 

Resin-Bound Iodine

There are several different resin filters that use iodine to disinfect water.  These work by forcing water through a iodine impregnated filter which kills microorganisms on contact. 

 

It is a novel approach, but has several shortcomings.  Since the treated water is colorless and lacks any iodine taste, it is impossible to tell if it has been exhausted of iodine.  Cold water decreases the speed of iodine disinfection and may necessitate double filtering.  These filters are also fragile and small crack may allow significant amounts of water to pass without being treated.

 Mixed Oxidants

Mixed Oxidants (Electrochemically Generated Oxidant Disinfection, EGO)

Electrolysis is used to produce hypoclorite or mixed oxidants from water and salt.  The mixed oxidants is a slurry of free chlorine, chlorine dioxide, and ozone and is often referred to under the company name MIOX.  This mix is effective against bacteria and viruses as well as Giardia and cryptosporidium oocyst with appropriate dose levels and treatment times.

 

MSR makes a portable MIOX system that requires table salt and small batteries.  It is EPA approved as a purifier and claims to treat Giardia in 30 minutes and crypto in 4 hours.  These times like the ones stated for chlorine dioxide are most likely very conservative and other testing shows a contact time of an hour as sufficient for cryptosporidium.  This device may be economically ideal over chlorine dioxide tablets for treating large amounts of water or for long periods of time.

 

Some testing suggests that using the overkill option (8x regular dose) and a 4 hour wait time is required to consistently treat for Crypto.

 

Metal ions

Metal ions of copper, silver and tin have long been know to have antimicrobial effects and used to treat boats and quite a number of health issues over the years.  It is also interesting to note that well water with copper or silver in it tends to be bright and clear and often free from turbidity from bacteria.  Due to new EPA guidelines that limit the amount of various heavy metals in drinking water, metal ion use has not caught on in the US.

 

Copper-Silver ionization

This has long been used to keep algae and shell growth off of ships and has been used to treat water.  Basically, the positively charged copper ions (Cu2+) in the water form electrostatic compounds with negatively charged cell walls of microorganisms. This affects cell wall permeability, causing cause nutrient uptake to fail and allows for an entrance for silver ions (Ag+). Silver ions enter the organism and bond to DNA and RNA, cellular proteins and respiratory enzymes, which disrupts cellular growth and cell division.

 Silver Ions

Silver Ions

Silver have been used for centuries to fight disease and purify water.  It is used in marine water storage tanks to stop growth of bacteria.  It is not effective against worm eggs, amoeba, or viruses.  Since it is slow acting (hours to treat) but doesn't gas off like chlorine, it is better suited for preventing bacterial growth in previously treated water that will be stored for long periods of time than it is for backpacker use.

 

Silver ions cause the release of K+ ions from microorganisms as well as bind with  nucleic acids proteins and other structures that effect cell life.

 

Silver isn't widely used to treat water in the US due to EPA guidelines that limit silver in drinking water to not exceed 0.10 milligrams per liter of water (0.10 mg/L).  Justification is due to concerns of argyria, a condition where skin turns blue from excessive consumption of silver. 

 

Katadyn Micropur uses silver ions with and without chlorine.  When the silver ion and chlorine combination is used, Katadyn claims that it will inactivate Giardia if given 2 hours of contact time.

 

Katadyn silver is a silver matrix used in some water filters.  This matrix is designed to stop bacteria from growing in the filter.  It does little in regards to disinfecting the water being filtered through.

 

Also see US EPA Silver Water Treatment.

 Potassium Permanganate

Potassium Permanganate (KMnO4, permanganate of potash, Condy's crystals)
Potassium permanganate is not as widely used as it once was as a water treatment.  It is not as effective as many less expensive treatment options and leaves a pink or brown color in water.

 

It is often used in survival kits since it can be used to sterilize water and wounds as well as be used as a chemical fire starter when mixed with glycerine, glucose or anti-freeze.

 

Usually 1 gram per quart (liter) is used for bacteria and viruses.  An alternative measuring system is based on water color after treatment.  Light pink for water treatment, dark pink as antiseptic and full red to treat topical fungal infections.

 

Also see US EPA Potassium Permanganate Water Treatment.

 

Hydrogen Peroxide (H2O2)
Hydrogen Peroxide is a poor choice for water treatment but has some disinfecting properties.  It is available in a variety of concentrations ranging from 3 to 90% and can be damaging if spilled on gear.

 

A 1.5% final solution may be necessary with 30 minutes of contact time.  Also of note, Fe+2 or Cu+2 need to be present as a catalyst for a reasonable concentration/time level.  Higher concentrations (10 to 30%) and longer contact times are needed to inactivate spores.

 

Due to the reactivity of concentrated hydrogen peroxide, it isn't recommended for backpacking use.

Other Chemical Treatments

There are many water treatment options that are not as widely used as those listed above.  These include:

 


Choosing a Water Treatment System

Backpackers have a lot of choices when it comes to figuring out how to get safe water.

 

Basics

  Viruses Bacteria Protozoa Particulate
Matter
Notes
Water filtration (1 micron or less) +++ +++  
           
Water filtration (0.2 micron or less) +++ +++ +++  
           
Water Purifiers ++ +++ +++ +++ Not always effective against viruses
           
Boiling water +++ +++ +++  
           
UV light +++ +++ ++ Effective against protozoa if given enough exposure to UV or if water is heated high enough to pasteurize
           
Chlorine Dioxide +++ +++ +++ Slow acting against protozoa
           
MIOX +++ +++ +++ Slow acting against protozoa
           
Chlorine +++ +++ + Not effective against Cryptosporidium
           
Iodine +++ +++ ++ Not effective against Cryptosporidium

Not recommended for long term use

 

+++ Effective
++ Limited Effectiveness
+ Some Benefit
No Benefit

 

Full Protection

If you want full protection against protozoa, bacteria and viruses, you will need on e of the following systems:

 

  Advantages Disadvantages
Boiling water
  • Available worldwide
  • Requires fuel or power
  • No residual protection
     
Chlorine Dioxide
  • Very compact
  • Inexpensive for short term use
  • Residual protection after treatment
  • Expensive if used a lot
  • Long treatment time needed for cold murky water
     
MIOX
  • Inexpensive for long term use
  • Residual protection after treatment
  • Expensive initial cost
  • Long treatment time needed for cold murky water
  • Anything electronic can fail
     
UV light
  • Simple to use
  • Expensive initial cost
  • Requires Batteries
  • Anything electronic can fail
  • No residual protection
     
Water filtration (1 micron or less)

and chlorine or iodine

 

Or Water Purifiers

  • Filters out suspended mater and helps with taste/odor
  • Residual protection after treatment
  • Bulky
  • Effort required to pump or set up filter
  • Chemical aftertaste
  • Filters require periodic maintenance or replacement
  • Many water purifiers don't work as well as advertised

 

Protection against Protozoa and Bacteria

For backpackers in alpine areas not touched by humans in the US or Western Europe, waterborne pathogenic viruses are less of a concern.  The following systems may be appropriate:

 

  Advantages Disadvantages
Water filtration (0.2 micron or less)
  • Filters out suspended mater and helps with taste/odor
  • Bulky
  • Effort required to pump or set up filter
  • No residual protection
  • Filters require periodic maintenance or replacement
  • Does not treat viruses
     
Boiling water
  • Available worldwide
  • Requires fuel or power
  • No residual protection
  • Kills everything
     
Chlorine Dioxide
  • Very compact
  • Inexpensive for short term use
  • Residual protection after treatment
  • Expensive if used a lot
  • Long treatment time needed for cold murky water
     
MIOX
  • Inexpensive for long term use
  • Residual protection after treatment
  • Expensive initial cost
  • Long treatment time needed for cold murky water
  • Anything electronic can fail
     
UV light
  • Simple to use
  • Expensive initial cost
  • Requires Batteries
  • Anything electronic can fail
  • No residual protection
     
Water filtration (1 micron or less)

and chlorine or iodine

 

Or Water Purifiers

  • Filters out suspended mater and helps with taste/odor
  • Residual protection after treatment
  • Expensive initial cost
  • Bulky
  • Effort required to pump or set up filter
  • Chemical aftertaste
  • Filters require periodic maintenance or replacement
  • Many water purifiers don't work as well as advertised

 

Minimal Protection (Bacteria and Viruses but not Protozoa)

Although not recommended for use while travel abroad, many backpacker wish to have a simple and minimal water treatment option for treating low risk water.  For backpackers who are drinking "safe" bottled or tap water and don't expect to run into an protozoan problems can use the following for the unexpected need for water purification:

 

  Advantages Disadvantages
Boiling water
  • Available worldwide
  • Requires fuel or power
  • No residual protection
  • Kills everything
     
Chlorine Dioxide
  • Very compact
  • Inexpensive for short term use
  • Residual protection after treatment
  • Kills everything with enough contact time
  • Expensive if used a lot
     
MIOX
  • Inexpensive for long term use
  • Residual protection after treatment
  • Kills everything with enough contact time
  • Expensive initial cost
  • Anything electronic can fail
     
UV light
  • Simple to use
  • Kills everything with enough contact time
  • Expensive initial cost
  • Requires Batteries
  • Anything electronic can fail
  • No residual protection
     
Chlorine or iodine
  • Residual protection after treatment
  • Very compact and inexpensive
  • Chemical aftertaste
  • Does not reliably treat for Giardia or Crypto
     
Water Purifiers
  • Filters out suspended mater and helps with taste/odor
  • Residual protection after treatment
  • Expensive initial cost
  • Bulky
  • Effort required to pump or set up filter
  • Chemical aftertaste
  • Filters require periodic maintenance or replacement
  • Many water purifiers don't work as well as advertised

 


Reference Articles and other information

Centers for Disease Control and Prevention (CDC)

 

U.S. Environmental Protection Agency (EPA)

 

World Health Organization (WHO)

 

US Army Center for Health Promotion and Preventive Medicine - Commercially Available Individual Water Purifiers

 

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