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, treating 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). At the other end of the world in New Zealand, 1,709 people contracted giardiasis in 2014 and New Zealand has the highest rate of giardia in the developed world (Wilderness Magazine NZ). Although, most NZ cases were from urban water supplies with viruses a lot less common in backcountry areas: 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 from creeks 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

Although, even in a wilderness area stagnant water or natural sources of pollution can be an issue…

You really want the entire catchment area of a river to be an unpopulated, and ideally, a wilderness area. Perhaps counter-intuitively, a fast-flowing stream is more likely to have a high concentration E.coli bacteria as the current will disturb river bed sediments. Heavy rain is also more likely to wash faecal matter from surrounding areas into creeks and rivers. Conversely, clear lake water is a better option as the ultraviolet wavelengths in sunlight kills faecal microbes – but collect the water near the surface, and away from any inlets (Wilderness Magazine NZ).

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.


Water treatment options

There are many options for treating water, 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

A 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 some contain affiliate links to outdoor camping stores which I recommend and which have competitive pricing.


Boiling is the simplest method to treating water, 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 way too many ways of boiling water to cover in this article, but here are some of the most popular stoves; JetBoil is ideal for quickly boiling water:

  • JetBoil Zip. Heavier than the MSR but includes an 800ml Cooking Cup; very quick to boil water.
  • MSR Pocket Rocket 2. Super lightweight – attaches to Isobutane | Propane gas canisters
  • Trangia 25-1 Large UL. Burns methylated spirit and includes two saucepans and frypan.
  • MSR Whisperlite International. Burns multiple fuels; one of the most versatile stoves but a bit more complicated than other systems.
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.

  • SteriPEN Classic 3 Water Purifier treats up to 150L on one charge and weighs only 82g. Lamp lasts for 8000 treatments.
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

Filtering water

There are many different type of filters for treating water, 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. I’d put this as my first pick for a gravity system.
  • 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. There’s also slightly cheaper 2L filter kit, but considering the marginal difference in weight and cost, the 2L is best.
  • MSR Hyperflow Micro Filter 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 0.5L in 10sec, and removes viruses, bacteria and protozoan cysts. The filter lasts about 300 uses (150L).  350g (10.9 oz). This is the one I recommend, unless you intend to filter large quantities of water (and you are not in an areas exposed to sewage).
  • Sawyer Mini is rated up to an incredible 378,000 litres (100,000 gallons) and is lightweight at 65g (2.5 ounces). The Sawyer pouch treats just under a litre (32 ounces / 0.95L). It needs regular backwashing to keep filter clean and won’t filter viruses. You can use it directly as a straw, use it in your bladder tube, or attach it to standard threaded bottles. The downside of the Mini is it prone to clogging; many recommend the Sawyer Squeeze, which is slightly more expensive and heavier (90g vs 65g) – it treats the same amount of water as its smaller sibling.
  • 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). The best choice if you are undertaking extended treks, especially in areas where the water quality is dubious, but not cheap.

Straw systems – filters as you drink

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

Chemical treatment

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.)

  • Katadyn Micropur Forte Water Purification Tablets use silver ions combined with chlorine. One tablet treats 1L, taking 30min for bacteria and viruses and 2hrs for giardia (in clear water).
  • Lifesystems Chlorine Dioxide Droplets (90g) uses chlorine dioxide to kill bacteria, viruses & cysts (including Giardia and Cryptosporidium) and leaves no after-taste. Treats up to 60 litres.
  • Katadyn Micropur Forte Water Purifier Liquid (100g) uses liquid ions combined with chlorine to treat up to 10,000L with one bottle (1 millilitre per 10L of water).
  • Aqua Prove Water Purification is less well-known, and uses chlorine dioxide to treat water. It’s not quite as easy to use as the other options, but has been recommended as leaving less of a taste in the water as the other tablets. (One tablet dissolved in the supplied 50ml bottle treats up to 50L.)
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 on treating water


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