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Water treatment methods

UV water treatment systems

I am currently researching ultraviolet (UV) water treatment systems and will be posting content soon.

Choosing a water treatment system

When it comes to choosing your own water treatment system, once you have read the postings on potential water contaminants and what might be in the water in your areas of travel, the next step is a deciding on what products to buy based on your requirements.

There are basically five systems with variations to choose from:

1) Portable microfilter in the form of a pump or gravity fed device, with or without a granular activated carbon (GAC) element

2) Portable purifier in the form of a pump, drinking straw device or a water bottle with a purifier element

3) A UV purification device

4) Chemical treatment by iodine, chlorine (water purification tablets), or a chlorine dioxide based system

5) A two step process combining chemical treatment with a microfilter, with or without a  granular activated carbon element

My preferred water treatment system is basically number 1 above. I use an MSR WaterWorks II (no longer manufactured) ceramic depth filter of 0.5 microns which has an internal granular activated carbon element as well as an integrated secondary 0.2 micron paper filter. This gives me absolute filtration down to 0.2 microns, which physically strains out all worm eggs, protozoa and bacteria. If I suspect the presence of viruses (see the section on trip planning) then I use system number 5 above.

I treat the water first with Polar Pure iodine and then after 30-60 minutes I pump the treated water through the MSR microfilter. The iodine inactivates any viruses and bacteria and the microfilter strains out all worm eggs, protozoa and bacteria and the GAC element in the filter removes the iodine. It’s a complete, virtually fail-safe system that produces clean, pure, fresh tasting water and is suitable for virtually any microbiological conditions. As a handy additional feature, the MSR WaterWorks II screws onto a standard Nalgene bottle for easy pumping thus eliminating the need to hold the bottle, pump and not fall in the river!

Amongst my other filter choices, I also occassionally use a Katadyn Pocket Filter which has a 0.2 micron ceramic depth filter. It basically substitutes for the MSR WaterWorks II filter but doesn’t have the handly screw fitting. Sometimes I also use a MSR MiniWorks filter which is the same as an MSR WaterWorks II filter with its 0.5 micron ceramic depth filter and GAC element but without the secondary 0.2 micron filter. All three of these microfilters have thick ceramic depth filters in them that can be scrubbed in the field and they will last for many thousands of litres before needing replacement.

To purchase any of my recommended products, please visit my shop.

Water treatment methods overview

Even after going to great lengths to choose the highest quality water sources possible, backcountry and recreational water should not be consumed without proper treatment.

The only exception is a situation in which you have no treatment system and there is a severe risk of dehydration.

Water treatment systems for the recreational travellers must be light-weight, cost effective and most importantly they must make water safe to drink under a variety of conditions.

The four types of treatment available for microorganisms are:

1) heat treatment (boiling)
2) chemical water treatments such as iodine
3) portable filters which are mechanical treatment devices containing microfilters
4) portable purifiers that combine microfilters, iodine impregnated elements, UV devices or other features.

The only viable portable treatment for chemically contaminated water is with a device that contains granular activated carbon (GAC).

Not all treatment methods are viable for all conditions so it is necessary to look at how different methods compare for different circumstances.

Heat treatment (boiling)

Heating water is the traditional method of water treatment.

It is the only method that is guaranteed to kill all microorganisms. It is important to note that heating water does not remove chemical contaminants or make seawater drinkable.

In the past, authorities recommended boiling water for 3–10 minutes plus one additional minute for every 330 metres (1000 feet) above sea level to account for the decline in boiling temperature at altitude. Recent research indicates that boiling time is irrelevant for all pathogens, except hepatitis A and B, which need at most one minute of boiling time, because by the time water reaches the boiling point of 100ºC at sea level, all harmful microorganisms have been inactivated or destroyed.

The reason for this is that the time required to kill or deactivate microorganisms  decreases exponentially as the temperature increases. Since the time required to boil water adds several minutes to the kill time, even at high altitude where the boiling temperature is lower than 100ºC, most pathogens are already dead by the time water boils.

Just to be sure, water should be brought to a rolling boil for two minutes before being consumed. If it isn’t possible to boil water, heating to above 55ºC for a prolonged period of time (see table below) perhaps by setting a container on a car dashboard or on rocks in hot and sunny conditions can go a long way towards making it safer to drink.


Bacteria are killed easily by heating water. Common pathogenic bacteria such as Salmonella and Campylobacter are destroyed in 30 minutes at 55ºC, less than one minute at 65ºC and instantly at 100ºC.


Viruses respond to heat in the same way as bacteria. Inactivation occurs in 20–40 minutes at 60C, less than one minute at 70ºC and almost instantly at 100ºC.

Notable exceptions are hepatitis A and B which are unaffected by temperatures as high as 56ºC and require about one minute at 100ºC to ensure deactivation.


Giardia, Cryptosporidium, E. histolytica and other pathogenic protozoa are killed easily and quickly by heat. Giardia cysts perish within ten minutes at 50ºC, five minutes at 55C and immediately in boiling water. Cryptosporidium and E. histolytica are killed at similar rates.

Parasitic Worm Eggs and Larvae

Worm eggs and larvae are also killed easily by heat. Eggs, which are more resistant than larvae, are killed at temperatures above 55ºC.

Below is a refernece table for heating times and temperature required to make drinking water safe from different pathogens. In all cases a rolling boiler for 2 minutes ensures that water is safe from pathogens.

Water Heating Temperatures and Times for Pathogens
Pathogen 55ºC 75ºC 100ºC (boiling at sea level)
Bacteria 30 minutes <1 minute Instant
Viruses except
Hepatitis A & B
30–50 minutes <1 minute Instant
Hepatitis A & B No affect <10 minutes 1–2 minutes
Protozoa 5 minutes 1–2 minutes Instant
Parasitic worm eggs & larvae 1–2 minutes <1 minute Instant

To Boil or not to Boil?

Ultimately, boiling is a highly effective method of ensuring that water is microbiologically safe to drink because it kills all harmful pathogens.

Boiling is particularly useful in areas that have high concentrations of human and animal waste because it guarantees that even the most dubious water can be made safe for drinking, although it might still have an unappealing taste.

Disadvantages of boiling as a primary method of water treatment include no effect on chemical contaminants and the burden of carrying large amounts of stove fuel or the environmental impact of open fires in some recreation areas. Hot water also has a low level of satisfaction in hot conditions unless you are making soup, tea, coffee or hot chocolate.

Introduction to chemical treatments

Many travellers, climbers and hikers favour chemical treatment because of lightweight and ease of use.

A bottle of iodine crystals, weighing less than a bottle of painkillers, can be tucked into any pocket and yet has the ability to treat hundreds or thousands of litres of water.

Currently, American-based manufacturers of chemical treatments are required to register them with the Environmental Protection Agency (EPA) Pesticide Branch. This guarantees product ingredients, proper labelling and that the product will perform its function without undue negative affects to the environment.

The EPA does not require manufacturers to substantiate claims about the effectiveness of their products with lab results and Health Canada currently has no guidelines applicable to chemical treatment products.

Generally, iodine and chlorine (referred to as ‘halogens’) are quite effective against all pathogenic microorganisms except Cryptosporidium and helminth eggs and larvae. Halogens have the advantage of low cost, lightweight, ease of use and passive disinfection. This means that you can add the halogen to water and go to sleep or hike a few kilometres while it does the job with no more effort on your part.

Halogens are also useful for keeping disinfected water pathogen-free while it is being stored in jugs or tanks on a sea kayaking trip or at a climbing base camp. Particularly when used with dehalogens, high concentrations of halogens are very effective for disinfecting water and keeping it disinfected until it is needed.

In the future, if portable chlorine dioxide products become cheaper and are shown by independent lab tests to be as effective in the variable conditions faced by travellers and trekkers as in municipal water treatment plants, and without health risks, they could quickly become the chemical treatment of choice.

Chlorine and Iodine (Halogens)

Iodine and chlorine, which work by oxidizing the cellular structures of microorganisms, are the most widely used chemical treatments.

Often referred to as halogens, they have been used for decades against bacteria and viruses however recently their inability to kill Cryptosporidium has been a topic of great concern. Halogens do not affect parastic worms eggs and are thus ineffective for treatment of water infected with parastic worm eggs.

Iodine and chlorine products do not neutralize or remove chemicals, elements or heavy metals from water or make seawater drinkable. They also leave residual chemicals in drinking water after treatment is complete.

Factors Affecting the Effectiveness of Chemical Treatments

Many environmental factors affect the effectiveness of chemical treatments in neutralizing pathogenic microbes.

Concentration and Exposure

Most important with iodine and chlorine are concentration, measured in parts per million (ppm) or milligrams per litre (mg/l) of water, and the exposure time of organisms to the halogen, usually measured in minutes.

Concentration and exposure have a direct relationship meaning that a greater halogen concentration reduces the time required to kill organisms, or alternatively, a longer time period allows for a reduction in the halogen concentration.

Water Temperature and pH

The colder the water, the higher the concentration needed, or the longer the contact time required.

The general rule is that for every 10°C increase in water temperature the ability of halogens to disinfect increases at a rate of two to three times. Thus, warm water is significantly better than cold water. The optimum pH for halogen use is 6.5 to 7.5 and most naturally occuring drinking water is within the acceptable range.

Contact Time

Generally the longer the contact time the halogen has with the water the better. Thus taken together, higher concentrations of halogens in warmer water for longer periods of time are more effective than lower concentrations in colder water for a shorter period of time.

Iodine and Chlorine Concentrations Required to Kill Bacteria and Inactivate Viruses at Different Contact Times and Temperatures
Concentration of halogen Contact time in minutes to temperature
5°C 15°C 30°C
2 mg/l (2 ppm) 240 min 180 min 60 min
4 mg/l (4 ppm) 180 min 60 min 45 min
8 mg/l (8 ppm) 60 min 30 min 15 min

*Note: data is correct for all bacteria, viruses, Giardia and E. histolytica but is not applicable to Cryptosporidium or parasitic worm eggs and larvae, which are impervious to halogens at typical treatment concentrations.

Turbidity and Other Matter

Water with high turbidity (suspended particles) from spring run-off or glacial rock flour can shield organisms and demands longer contact times. More importantly, vegetative matter such as humus, nitrogen rich organic and inorganic substances such as amino acids from faeces and nitrites and nitrates from fertilizer, can adsorb or react with halogens. This reduces the halogen concentration and thus the halogen’s ability to kill pathogens.

In basic terms, halogens work best in clear water.

Typical Halogen Demand for Different Types of Water
Water Source
Halogen Demand (mg/l)
Clear alpine water 0.3
Cloudy river water 3–4
Pond water 5–6
Municipal wastewater (sewage) 20–30

*Note: This information depicts only average conditions and should not be taken as a guide for local conditions, which can vary widely.

Pathogen Type

While bacteria and viruses are killed relatively quickly by halogens, protozoa, such as Giardia and E. histolytica, are more resistant and require greater halogen concentrations or contact times. Cryptosporidium, and most helminth larvae and eggs, are too resistant to be killed reliably by halogens under most field conditions.

Exposure to Air and UV

Exposure to air and sunlight (UV radiation) greatly reduces the effectiveness of halogens.

Purification tablets that rely on chlorine are extremely susceptible to UV radiation and exposure to air. They can lose their potency in hours or days. Tablets should be keep tightly sealed in the manufacturer’s container and should be replaced before every major trip or every six months. In other words, do not use last year’s tablets this summer.

Adequate Halogen Doses

When using halogens while hiking few factors are controllable. Warm clear water is infinitely preferable to cold cloudy water rich in vegetative matter or sediment. Follow the instructions provided with whatever product you are using for your water conditions, or consult the following chart for guidelines of concentrations and waiting times. Liquid iodine solutions and chlorine, in the form of household bleach, should be added to water with an eyedropper.

Iodine and Chlorine Doses
Halogen Type
Target Dosage
4 mg/l (4 ppm)
Heavy Dosage
8 mg/l (8 ppm)
Iodine tablets, Portable Aqua (trade name) ½ tablet 1 tablet
2% Iodine solution (tinture) 0.2 ml, (5 drops) 0.4 ml, (10 drops)
10% Providone iodine solution 0.35 ml, (8 drops) 0.70 ml, (16 drops)
Saturated iodine crystals in water, Polar Pure
(trade name)
13 ml 26 ml
Chlorine household bleach (5% sodium hypochlorite) 0.1 ml, (2 drops) 0.2 ml, (4 drops)

*Note: Iodine and chlorine are effective against bacteria, viruses, Giardia, E. histolytica, but not against Cryptosporidium or parasitic worm eggs and larvae.

Health Risks of Halogens

Iodine is a potentially dangerous substance that can have both short and long term effects on human health. While the body requires iodine in very small amounts, large doses— two to four grams of free iodine—can be lethal.

Even much smaller amounts can cause severe problems for people allergic to iodine, those with thyroid disease, and fetuses in pregnant women. Opinions vary, but authorities seem to agree that most people, with the exception of those just mentioned, can safely ingest iodine at levels required for water treatment for periods ranging from three weeks to two months without affecting their health.
Chlorine, whether in the form of water treatment tablets or household bleach, is not generally toxic even at levels as high as 90 ppm. Long term low intensity use has no known affects on humans as evidenced by the worldwide use of chlorine in municipal water treatment systems, although recently some researchers have tentatively linked chlorine use to kidney cancer. At very high concentrations, such as in raw household bleach, chlorine is corrosive to human flesh and direct contact should be avoided.

Odour and Taste

Sensitivity to the odour and taste of iodine and chorine varies widely among people. Some people are unable to choke down chemically-treated water while others guzzle it unfazed. Odour and taste can be overcome or masked in a variety of ways.

  • Decrease the halogen dose and increase the exposure time. This allows for a lower concentration of halogen in the treated water. Letting cloudy water settle before treatment and warming cold water in the sun will help reduce the dose required to disinfect.
  • Using a granular activated carbon filter after treatment will remove virtually all traces of iodine and chlorine from treated water.
  • Resting an open water container in the sun will allow UV radiation to reduce chlorine concentrations in treated water.
  • Add a dehalogen to the water after treatment to remove halogens. Dehalogens include hydrogen peroxide, sodium thiosulfate and ascorbic acid (vitamin C) often found in drink crystals, which has the added bonus of flavouring the water.
  • Hold your breath and swallow.

Potassium Permanganate

This agent is used widely in the developing world for water disinfection and for washing fruits and vegetables. The compound is readily available outside of North America.

Lab research has verified potassium permanganate’s effectiveness against bacteria and some data suggest effectiveness against viruses. There is no information about how effective it is against protozoa or helminth eggs and larvae.


Silver ion appears to have an anti-bacterial effect in very low doses and is sometimes used with mixed results in filters or purifiers to limit bacterial colonization within devices, but not as an anti-bacterial agent. Little is known about silver’s effectiveness against viruses, protozoa, and helminth eggs and larvae. This lack of information, the cost, and possible negative health effects, currently make silver ion a marginal choice for water treatment.

Chlorine Dioxide

The most exciting and potentially important development in chemical treatment products was the introduction of a chlorine dioxide based treatment to the market, in 1999, under the trade name Aquamira.

To treat water, the user combines liquids from two separate bottles to produce a mixture, which is added to water. The mixture gives off chlorine dioxide gas, which is not a halogen but rather a powerful oxidizer unrelated to chlorine that has been used for decades in municipal water treatment systems.

Research from municipal water treatment plants suggests that chlorine dioxide has the potential to be an outstanding treatment product for backcountry and recreational travellers.

Not only does it kill bacteria, viruses, and protozoa, including Cryptosporidium, there are also no health risks because the only byproducts it leaves in drinking water are oxygen and a miniscule amount of salt.

Furthermore, from industrial usage, it is known that chlorine dioxide has the potential to reduce or eliminate some chemical contaminants, possibly including pesticides, nitrites and sulfites.

Although chlorine dioxide seems to be vastly superior to chlorine and iodine and its effectiveness against microorganisms has been proven in large water treatment plants, there are no independently verified lab results available yet to substantiate its effectiveness under recreational field conditions. This is particularly true with regards to chlorine dioxide’s ability to eliminate some chemical contaminants from water and its effectiveness, if any, against parasitic worm eggs and larvae. Chlorine dioxide products are also expensive in terms of the amount of water it treats compared to iodine and chlorine.

My preferred water treatment system

After more than 15 years and across a dozen countries, the treatment system I use has continued to keep me and my companions free from waterborne sickness. While my method works has worked for me, you shouldn’t adopt it without considering your own geographic and topographic situation and the types of trips you are planning.

My trips have largely been in mountain areas of North America, Western Europe, the Atlas Mountains of Morocco and New Zealand. Many of these areas have high quality alpine water sources though there is often a significant human and animal presence.

The greatest risks are from Giardia, Cryptosporidium and to a lesser extent bacteria and viruses. There is a small risk of helminth eggs or larvae because of the sheer number of tourists in some areas. There is also the possibility of chemical contamination from ranching, forestry and mining activities.

By examining topographic maps, before heading on trips I’m aware generally aware of current and historical mining activity and the locations of towns, sewage treatment facilities, septic fields and backcountry huts and campgrounds. This knowledge helps me to avoid drinking water downstream from these possible sources of contamination.

I also obtain current local information when possible. In the backcountry, I keep on the look out for animal and human faeces, the frequency of other travellers on the trail, especially those with dogs and the proximity of backcountry campgrounds and toilet facilities to water sources. Above all, I strive to take my drinking water from as high up in the alpine as possible and always from above areas of human activity.

For treatment, I generally rely on a MSR Waterworks II microfilter with a ceramic element that has an absolute 0.5 micron pore size, a built-in GAC element and a secondary paper filter with an absolute pore size of 0.2 microns. In theory, this device should remove all microorganisms down to 0.2–0.3 microns including bacteria, protozoa, and any helminth eggs or larvae. The GAC element removes any offensive taste from the water although mountain water is usually clear and tasteless.

Since pathogenic viruses are generally only present in areas with people, I usually take the risk that the water is virus free or that viruses are clumped together with particles that can be filtered. On occassion I feel that specific water is risky because of a campground or climbers’ hut upstream, the prevalence of human occupation or because I’m drawing water from a river or lake draining a large area. In such cases I first filter the water to remove visible organic matter and silt if necessary. I then treat the water with Polar Pure iodine and let it sit for 20-30 minutes to kill bacteria and inactivate viruses before pumping it through the filter again so the GAC element can remove the iodine.

I’ve used this method effectively in many places including areas with huge herds of livestock. This combination of microfiltration and halogen treatment is so effective that I’d recommend it for all but the most arduous conditions. The exception is areas with high levels of chemical or heavy metal contamination where no portable treatment system will be 100% effective. On my adventures, I rarely filter water used for soup, tea or coffee because boiling the water instantly kills all pathogens.