Water purification: Essential tips for hiking

The pros and cons of water purification methods

Water is essential for survival, but how long a person can go without it varies widely depending on temperature, activity level, health, and access to shade. In hot or exposed conditions, dehydration can become life-threatening within a day, while in cooler environments survival may extend longer. Because untreated water can carry serious health risks, understanding reliable water purification methods is critical when hiking. Choosing the most appropriate method depends on your environment, equipment, and available time, and taking unnecessary risks with untreated water should always be avoided.

Untreated water may contain bacteria, viruses, protozoa, or parasites that are invisible to the eye and can cause gastrointestinal illness, dehydration, or prolonged sickness. In remote areas, even a minor waterborne illness can quickly become serious by limiting your ability to walk out, manage exposure, or make sound decisions. Clear, fast-flowing water is not always safe, and contamination can occur well upstream from where you collect it. On multi-day walks, preventing illness is often as important as avoiding injury.

With those risks in mind, the following methods outline the most common and reliable ways hikers can make water safer to drink, along with their strengths and limitations.

Boiling

Boiling is one of the most reliable ways to make water microbiologically safe. It effectively kills bacteria, viruses, and protozoa that can cause illness. In most situations, bringing water to a rolling boil for at least one minute is sufficient. At higher elevations, where water boils at a lower temperature, a longer boil time of around three minutes is recommended. Boiling does not remove chemical contaminants or heavy metals and requires fuel and time, which may be limiting factors in some situations.

Bleach

I’m not a big fan of ingesting chemicals, but liquid household bleach can be used to disinfect water when no other options are available. The bleach must be free of additives and scents and should contain a hypochlorite solution of at least 5.25 percent. If the water is clear, add 2 drops of bleach per litre of water. If the water is cloudy, add 4 drops per litre. After adding bleach, stir the water and allow it to stand for at least 30 minutes before use. Bleach is effective against bacteria and viruses but is less reliable against some protozoa. Taste can also be affected, and care must be taken to measure doses accurately.

Water purification tablets

Water purification tablets can be an effective option when used correctly and according to the manufacturer’s instructions. Different tablets use different active ingredients and require specific contact times to be effective. Always check the instructions on the packaging and be aware of expiration dates, as older tablets may be less effective. While tablets can treat many microorganisms, some types may not be effective against all parasites, and treated water may have an altered taste.

Water filters

This is my go-to solution when possible. Commercial filters are available in a wide range of sizes, styles, and capabilities. I previously favoured lightweight squeeze filters such as the Sawyer Mini, which offers excellent filtration, very low weight, and an impressive lifespan on paper. However, after several years of regular use, I have largely shifted to the Katadyn Hiker Pro.

While it is heavier and bulkier than Sawyer-style filters, I have found the pump design maintains a more consistent flow rate over time, particularly in natural water sources with fine sediment. With squeeze filters, I occasionally struggled with reduced flow or difficulty drawing water, which may come down to technique or maintenance but can still be frustrating in the field.

Katadyn and MSR both manufacture highly regarded pump-style filters, and for many hikers the trade-off in weight is offset by reliability and ease of use. During an extended emergency, it is also important to understand how to improvise a basic pre-filter using materials such as cloth, sand, and charcoal. A quality filter remains one of the few methods capable of removing most biological contaminants, particularly bacteria and protozoa, while also improving taste and clarity.

UV water purifier

UV water purifiers can be effective when used correctly, but they have important limitations. They require batteries or charging, only work with clear water, and typically treat small volumes at a time. UV treatment inactivates many microorganisms but does not remove sediment or chemical contaminants. For these reasons, UV purifiers are best used as part of a broader water treatment strategy rather than relied on as a sole method in remote or emergency situations.

SODIS

Solar water disinfection, or SODIS, uses sunlight and clear PET plastic bottles to inactivate microorganisms in water. It can be effective under the right conditions, typically requiring several hours of strong sunlight and relatively clear water. SODIS does not remove chemical contaminants and is dependent on weather, daylight hours, and temperature. While it can be useful in some survival situations, it is slow and produces limited volumes of treated water.

Distillation

One of the most effective means of purifying water is distillation, though it is far from convenient. Distillation requires staying in a fixed location and a degree of ingenuity. A traditional still, similar to those used for alcohol production, can produce significant quantities of purified water but requires specific equipment and a fire, which may not always be practical or desirable. Solar stills are another option in certain environments and conditions. The major advantage of distillation is that it removes virtually everything, including bacteria, viruses, protozoa, heavy metals, and many chemical contaminants. The downside is the time, effort, and setup required, making it unsuitable for most routine hiking situations.

Final thoughts

Access to safe drinking water is not something to take lightly when hiking, particularly in remote or multi-day settings. No single purification method is perfect, and each comes with trade-offs around weight, speed, reliability, and effectiveness. Understanding those limitations is just as important as carrying the equipment itself.

In practice, the best approach is often a flexible one. Boiling and quality filters remain among the most reliable options, while chemical treatments, UV devices, and SODIS can play a role when conditions allow. The right choice will always depend on where you are, the water sources available, and what you are prepared to carry.

Planning ahead, maintaining your gear, and knowing how to adapt when conditions change can make the difference between a minor inconvenience and a serious problem. Safe water supports clear thinking, good decision-making, and the ability to keep moving, all of which are essential in the outdoors.