Guide to Treating Water

It’s not so much an issue for day-walks, as you can generally carry all the water you need… But for multi-day walks, having the ability to treat water is pretty much essential. (Even on a shorter walks, carrying a water filter or a means of treating water allows you to travel a lot lighter.)

The importance and need to treat water – and the type of treatment – will depend on where you are hiking. In remote backcountry areas you should be able to drink from streams with no treatment – although this is arguably becoming riskier. For example, in the US giardia is now considered to be endemic in the western mountain regions such as the Rocky Mountains, Sierra Nevada, Cascades (although this has been disputed). Conversely, viruses are less common in backcountry areas and a more prevalent threat in developing countries. While on a Tongariro Circuit tramp in New Zealand, signs at one of the huts encouraged hikers to fill up their water bottles at a natural spring (below), a short walk away.

To treat, or not to treat?

Around urban areas, signs of pollution are generally pretty obvious – and you’re probably not going to need or want to drink water on a suburban bushwalk. But even in remote areas, determining the quality of a water-source can be difficult. The presence of foam may be an obvious sign of pollution – but equally it may be naturally caused by surfactants, such as dissolved organic matter. Conversely, a crystal-clear river running through a wilderness area can be polluted by urban run-off a long distance upstream.

If a flowing stream looks clear and has no discernible odour, the only somewhat reliable way to ensure it is safe to drink is to check on a topographical map that there upstream of the collection there are no:

  • Camp sites
  • Farms or agricultural areas
  • Urban areas
  • Mines or areas where mining has taken place

You really want the entire catchment area of the river to be an unpopulated, and ideally, a wilderness area. Although, even in a wilderness area stagnant water or natural sources of pollution can be an issue…

Pollution types

Micro organisms (protozoa, bacteria and viruses) from human and animal faeces are the most common form of pollution (75-80% water pollution is caused by domestic sewage):

  • Protozoa (cryptosporidium and giardia being the two most common) are parasites that are found in the faeces of infected humans and animals. Infection causes gastrointestinal illness, such as diarrhea and vomiting. The average incubation period is 7 days, so it’s unlikely you’ll show any symptoms a day or two after drinking contaminated water.
  • Bacteria (eg. E, Coli, salmonella) are similar to protozoa but smaller, and also found in human and animal faeces. The incubation time is generally 2-5 days, with symptoms including cramps, nausea, diarrhea and headaches. As with protozoa infections, there is no treatment available (other than rest and staying hydrated).
  • Viruses (eg. hepatitus, norovirus) are smaller again, and are a major cause of human waterborne and water-related diseases. Sewage-contaminated water many contain one hundred different species of virus. Although the incubation period is highly variable (depending on the virus), symptoms are normally developed within 12-48 hours.

Chemicals are generally the result of run-off from agriculture, which is the leading cause of water degradation globally. Nutrient pollution can cause algal blooms,  which can be harmful even if not visible (less of a risk with running water). Mining can also leave heavy metals in the water, which may be around well after mining operations have ceased.


Treatment options

There are many treatment options, some of which work better in eliminating certain pollutants. The only method that pretty much works on everything is boiling.

Protozoa Bacteria Viruses Chemicals / Metals
Boiling Yes Yes Yes No
UV Light Yes Yes Yes No
Filtering Yes Yes No (except a few models) Varies
Chemicals Partially effective Yes Yes No

Detailed PDF download comparing treatment options is published by the US Center for Disease Control and Prevention (CDC).

Disclaimer: The links to products below are personal recommendations, and may contain affiliate links to Wild Earth – one of several outdoor/camping stores that I trust and buy most of my gear from.


The simplest method, although not always practical if you need water during the day. Boiling is effective against most microbial contaminants, with protozoa cysts killed at about 55 C / 131 F and common bacteria and viruses (including E. coli and Hepatitis A) being killed rapidly at temperatures at or below 65 C / 149 F.

There are too many ways of boiling water to cover in this article, but a couple of cooking stoves ideal for quickly boiling water are:

  • JetBoil – compact gas-canister stove that can boil 500ml of water in 2min
  • Whisperlite multi-fuel stove can boil 1L of water in 3.5min (using white gas)
Pros Cons Best for…
  • Nil cost if you’re already carrying a stove
  • Highly effective treatment method
  • Can be inconvenient / time consuming
  • Water needs to be cooled before drinking
  • Overnight camping

UV Light

UV Purifiers (eg. SteriPEN) work by using an ultraviolet light which kills pathogens, including viruses. They can use batteries or are USB-chargeable. The manufacturer claims a reduction of at least 99.9% of bacteria, viruses, and protozoa, a claim that has been validated IF the device is used correctly. However, it’s critical that a UV purifier is used correctly and the water being treated is clear, or it’s effectiveness can significantly impacted.

Pros Cons Best for…
  • Quick to use
  • Effective on all micro organisms (germs)
  • Won’t add any taste to water
  • Won’t work in cloudy/muddy water
  • Useless if not charged / batteries flat
  • Fragile light bulb
  • Day walks
  • Shorter overnight hikes


There are many different type of filters, which all need some form of pressure to force water through a filtering system. This generally means gravity, manual pumping or sucking water through a straw. The filtering system may be a mechanical system, activated carbon or a combination of both. For groups, consider a gravity system (some filter up to 10L at time), while for personal use there’s a lightweight model in each category, depending on your preference.

One of the drawbacks of mechanical filters is they won’t remove viruses, which are smaller than the size of the 0.1-micron microfilters typically used. There are a few different Grayl and Lifesaver models (USD$50-$160) and the much more expensive MSR Guardian Water Purifier (USD$500) that remove viruses using a more sophisticated filtration system. The Grayl Ultralight Purifier is my pick, and one I take it on just about every long hike (I use it once a month on average and change the filters every couple of years).

Gravity systemsuses gravity to move water through a filter

  • Katadyn BeFree Water Filtration System 3.0L filters up 2L per min (but collapses to a small size) – a good option for larger groups. Only weighs 113g (4 oz). A smaller 1L version also available as well as a larger 10L system for groups. The filter lasts up to 1000L.
  • Platypus Gravity Works 4L filters four litres in 2.5 minutes, but at 326g (11.5 oz) it weighs a bit more than the similar Katadyn system. The filter lasts 1500L.
  • MSR Trail Base Water Filter Kit combines a gravity filtration system for camping with a small filter to use when hiking. Filters 1L per min and filter life is 1500L. Heavier system weighing 620g (1 lbs 6 oz).

Pump systems – you push or squeeze the water through a filter

  • Grayl Ultralight Purifier treats 473 ml (16 oz) in 15 sec, and removes viruses, bacteria and protozoan cysts. The filter lasts about 300 uses (150L).  309g (10.9 oz)
  • Lifesaver 4000 Ultra Water Filtration Bottle is very similar in concept to the Grayl bottle. It also removes viruses, with its microbiological water filter lasting up to 4,000L. Treats up to 750ml and weighs approx 1kg.
  • Sawyer Micro Squeeze is rated up to an incredible 378,000 litres (100,000 gallons) and is lightweight at 70g (2.5 ounces). Pouch treats just under a litre (32 ounces / 0.95L). Needs regular backwashing to keep filter clean and won’t filter viruses.
  • MSR Trail Shot is one of the smallest and lightest models. It filters 1L per minute and weighs just 142 g (5 oz). Cartridge (filter) life is 2000L.
  • MSR Guardian Water Purifier is the Rolls Royce of water filters, removing pretty much everything. Treats 2.5L per min with a cartridge life 10,000L+ and is self-cleaning. One of the heaviest ‘though at 490g (1 lbs 1.3 oz)

Straw systems – filters as you drink

  • LifeStraw Personal is the original “straw” – lightweight (57g / 2 oz), inexpensive and lets you drink directly from streams, lakes or any container. Filter treats 4000L.
  • LifeStraw Flex combines a LifeStraw with a squeeze bottle. Microbiological filter lasts up to 2,000L; and replaceable carbon capsule up to 100L.
Pros Cons Best for…
  • Easy to use
  • A few models will remove all germs
  • Removes sediment & chemicals
  • Filters need replacing
  • Less effective with dirty water (can clog filters)
  • Most models don’t remove viruses
  • Day walks
  • Overnight camping
  • Multi-day hikes


Purifying chemicals (such as iodine, silver or chlorine) that kill living organisms in water can be added as a liquid or tablets to water, and typically take 1-2 hours to be effective. Giardia and cryptosporidium are resistant to chemical treatments, although many purification tablets combine chemicals and claim to kill both giardia and cryptosporidium. (To be really sure, you can combine chemical treatment with filtration, as protozoa are generally larger than most filters.)

Pros Cons Best for…
  • Lightweight
  • Easy to use.
  • Can be 20-30 minute delay before drinking
  • Not safe for pregnant women
  • May leave aftertaste
  • Long multi-day hikes
  • Backup for other methods
  • Places where water is very likely to be contaminated

Research and References

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