Person using a gravity water filter in the forest

About water treatment, filters and purifiers

When you’re hiking in the backcountry, all water sources – pristine-looking lakes, fast-flowing creeks and glacier-fed streams – can be contaminated by birds, animals or humans. International travellers also need to be aware of illnesses that can come from contaminated water, even if it looks clean.

Simply put, if your water is from an untreated or questionable source, you should treat it before you drink it, cook with it or use it to brush your teeth.

The cleaner the water is at the start, the more effective any treatment method will be. When you select a water source, avoid standing water if you can, and use the clearest water available. If you have to collect water that looks cloudy or muddy, let it settle in a pot or bucket, and skim or siphon off the clearer water to treat it.

Micro-organisms that cause illness

Disease-causing micro-organisms (pathogens) in water that are the most concerning are:

  • Protozoa include cryptosporidium and giardia (the cause of giardiasis or “beaver fever”). Protozoa are increasingly widespread in North America.
  • Bacteria exist in water all over the world. Most are harmless, but some cause sicknesses such as diarrhea and dysentery. They are smaller than protozoa.
  • Viruses cause hepatitis, polio and other diseases. They can be present in any water contaminated by human waste, and are extremely tiny – smaller than bacteria or protozoa.

How to treat water for hiking or travel

The most common ways to treat water for drinking and cooking are:

  • Filtering water
  • Chemical treatment (via tablets or drops)
  • Purifying water (combining filters and chemicals)
  • UV-light purification
  • Boiling water

People often use filters and chemicals together to make sure all pathogens are dealt with, in case some are resistant to one of the methods (particularly viruses, which are the smallest). It’s always a good idea to have a backup method of treating water, such as boiling water, in case something happens to your primary method of treatment.

Water filters

Water filters strain out pathogens when water is forced through them. Many filters you pump by hand, some are built directly into drinking bottles, and large units let gravity do the work for you.

Filters remove protozoa and some larger bacteria; if you want to remove most or all bacteria you’ll need a filter with fine pores. Viruses are many times smaller than bacteria, so most filters cannot remove them. If you’re travelling to countries where viruses are a risk in water, it’s best to use filters along with chemical treatments.

  • Great where viruses are not a concern, or for occasional users and short trips.
  • Pump filters are good for small groups, while gravity filters can filter bigger amounts of water for basecamps or large groups.
  • Filters can fail or be damaged by impact. Many people carry compact water treatment tablets as a back-up.

Water treatment tablets and drops

Chemicals generally don’t take up a lot of space and are easy to use. They’re effective against bacteria and viruses. But some protozoa, including some cryptosporidium, are resistant. Chemicals don’t require any pumping, but they do require time to act – from a few minutes to several hours, depending on how cold or dirty the water is, and which pathogens you want protection against.

Chemicals are good for short-term use: days or weeks, rather than months at a time. Tablets are common in many emergency kits, and many have a decent shelf life. For many, the health risk associated with small amounts of exposure to chemicals is outweighed by the benefit of protection against pathogens. But for pregnant women, young children or anyone with a pre-existing health problems, this may not be true. It’s best to consult your doctor before using chemical water treatments.

  • Chlorine dioxide doesn’t leave any unpleasant taste or odour in your treated water. Since it’s unstable, you prepare it in the field by mixing two chemicals together. The active ingredients in chlorine dioxide break down quickly, so it usually won’t kill beneficial micro-organisms in your digestive system.
  • Chlorine kills many of the micro-organisms that help you digest food, resulting in digestive trouble. In water, chlorine also forms some by-products that are suspected carcinogens.
  • Iodine is inexpensive, lightweight, and comes in easy-to-use drops or tablets (though it’s less common these days). Many people use it in combination with a water filter to reduce the taste and odour that makes iodine treated water hard to drink.

Water purifiers

If you’re facing water that possibly contains all the pathogens – bacteria, viruses and protozoa – it makes sense to use a combination of chemical and filter treatments. There are portable systems that do just that.

The capacity to protect against viruses is what distinguishes a purifier from a filter. Purifiers are available in two systems: a single-step self-contained unit or a filter with a separate chemical treatment.

  • Single-step purifiers are fast, simple and easy to use. The water passes through one or more filters and then through a matrix with a chemical. Be sure to read the instructions to understand how to pump the water so it’s properly treated.
  • Purifier systems take a bit more effort, but also provide greater certainty that the viruses have been exposed to enough chemical to inactivate them. They contain a regular filter unit and a separate chemical added to the water after it’s been filtered.
  • Both options are economical over the long term. Suited to frequent users, extended trips, and larger groups.

UV-light purifiers

A discreet and portable way to treat 0.5 or 1L of water at a time when you’re travelling. By beaming UV light through water, they damage the DNA of microbes, pathogens and viruses. It’s the same technology used in commercial bottling plants and municipal water systems.

  • They avoid the taste, health concerns, and waiting times of chemical treatments.
  • Don’t require pumping, and don’t need to be dissembled and dried when you return home.
  • Cloudy water must be filtered before you use UV. Some include pre-filters.
  • Most use batteries, so you’ll need to carry spares or a solar re-charging system.

Boiling water

Enough heat will destroy all pathogens, so boiling water is reliable. But it’s not a popular method as it consumes time and fuel, and boiled water has a flat taste. So, except for cooking water, most people choose to treat their water with filters, chemicals or both.

  • Recommended times range from 5 to 20 minutes.
  • Higher elevations require slightly longer boil times.

Caring for water filters

Silty water (often found in glacial regions) clogs filters and makes pumps more difficult to operate. To make pumping easier, let any silt settle for an hour or two before pumping the water.

Read the manufacturer’s instructions carefully to know how to care for your water filter. In most cases, filters should be taken apart and left to air-dry to help prevent mildew and bacteria growth. They can be cleaned many times with a brush before needing to be replaced, but clean them only when necessary to prolong their life.

Cost effectiveness

Generally, the lower the initial cost for a treatment method, the higher the cost of each litre treated.

  • If you camp occasionally and in a small group, a moderately priced filter with a semi-disposable cartridge, combined with a small chlorine dioxide kit, may be fine.
  • If you camp frequently, or with a large group, it may be more economical in the long run to buy a more expensive filter.
  • Inexpensive filters clean a few dozen to a few hundred litres. A high-end filter might clean thousands of litres.
  • A UV purifier with rechargeable batteries can treat 3,000-8,000 litres.

For more information on safe water when you’re travelling, check out Health Canada’s travel health and safety info.