How to Purify Water in the Wilderness

Potable water is of the utmost importance on any wilderness journey. Given that water is fairly dense at 1 kg/L, carrying a sufficient water supply on your back can be impractical. Finding water along the way is necessary for a journey covering any substantial distance.

Unfortunately, most naturally occurring freshwater sources are not potable without some form of treatment. Parasites like Cryptosporidium and Giardia are widespread in freshwater sources across the world. Catching these parasites can lead to highly unpleasant intestinal problems, and serious illness in some cases.

The primary ways to purify freshwater while hiking/camping are:

1. Filtration
2. Chemical disinfection (purification tablets)
3. Boiling

To be absolutely certain that your water source is safe to drink, you can combine these methods in succession. For example, filter then boil, or filter then use purification tablets.

Purifying salt water requires additional techniques, such as distillation or reverse osmosis, which are not covered here.

Selecting a Water Source, Pre-Filtering

When possible, try to gather water from a moving water source. Stagnant water is more likely to harbor harmful parasites. If you are traveling in an area with known springs, use them! Springs tend to be the highest quality water source available.

If the only water available is stagnant or turbid, consider using a shemagh, a bandana, or other piece of cotton fabric to pre-filter your collected water.

To prefilter water with a shemagh, stretch the shemagh tightly over the lid of your collection container (for example, a Nalgene). You can secure the cloth to the container with a piece of bank line or other cordage. Submerse the container, collecting the water through the shemagh and into the container.

Pre-filtering with this method will not disinfect the water source, but it will filter out heavier particulates, and potentially remove some unwanted tastes from the water. You must subsequently purify the water by boiling, chemical disinfection, or by using a more powerful filter.

Filtering

There exist several filter products that can effectively remove harmful parasites from water. Ensure you select a filter with a sufficiently small pore size (1 micron or smaller). Whichever filter you choose, be sure to follow the manufacturer's instructions to produce the safest possible drinking water. Here are some of the best choices for filters:

LifeStraw

The LifeStraw can be used to suck water directly from a contaminated source, or by first capturing some dirty water into a container, then siphoning the water from your container through the LifeStraw. It is lightweight, and will provide you with 4,000 liters (1,000 gallons) of safe drinking water with proper cleaning/maintenance.

Sawyer Mini

The Sawyer Mini is a slightly smaller alternative to the standard LifeStraw. It comes with a dirty water collection bag that threads onto the filter, which means you can squeeze water from the collection bag through the filter and into a container for drinking. You may find this preferable to the LifeStraw, which requires that you use your own suction to pull water through the filter.

LifeStraw Flex Advanced Water Filter with Gravity Bag

If you will be establishing a base camp, consider using a product with a gravity bag. You can gather several Liters at a time in the bag, and filter it into drinking containers by hanging the bag from a tree. The gravity feed method results in a relatively slow drip through the filter, so it will take some time to fill your container. You can handle other tasks around camp while you wait for your container(s) to fill with potable water.

DIY Water Filter

In an emergency/survival situation, you can fashion your own water filter using natural materials like charcoal, sand, pebbles, and grass. You can find instructions on how to make such a filter here.

If using a DIY filter, there is a higher risk of contracting unwanted bacteria or viruses. In a normal hiking/backpacking/camping situation, you should not have to resort to a makeshift water filter. You should instead strive to be adequately prepared before you set out on your journey.

Purification Tablets

Tablets offer the most compact method of purification. If you traveling ultralight, this is a method to consider. You simply add a tablet to your water-filled container, wait for a duration specified by the manufacturer, and your water is potable. Typically, tablets will impart a mild chemical taste on the water.

We do not recommend using an iodine-based tablet for purification, as better alternatives exist. Iodine is not considered effective in eliminating Cryptosporidium from drinking water. Iodine should not be used by pregnant women, people with thyroid problems, or people with iodine hypersensitivity, nor is it recommended for continuous use (more than a few weeks at a time).

Instead, look for a chlorine dioxide tablet. Chlorine dioxide tablets are generally more expensive, but worth the extra assurance that you won't have to deal with a serious intestinal infection on the trail, or when you return home.

These are two of the best water purification tablets available on the market (both of which are effective against Cryptosporidium):

Katadyn Micropur MP1 Purification Tablets

Potable Aqua Chlorine Dioxide Water Purification Tablets

Boiling

Boiling is a surefire way to kill bacteria and parasites present in your water source. However, it will not remove any unwanted chemical/industrial elements, which is why a combined method such as filtering followed by boiling is the safest choice.

To ensure you can boil water in any situation, you should carry:

• An all-metal container made of stainless steel or titanium. Titanium is lighter than stainless steel, but more expensive. Ensure your container does not have any plastic components, so it can be used directly over a fire if needed.

  

  A titanium pot is lightweight and highly inert, meaning it won't impart harmful chemicals on its contents when heated.

• A small gas stove, especially if the ability to make a fire on your trip is in question, or disallowed by regulations.

  The lighter-weight stove option is an isobutane canister (or butane/propane mix) coupled with an appropriate burner. The burner threads directly on top of a fuel canister, then you can place your container on top of the canister/burner assembly for boiling.

  Be aware that isobutane stoves are usually sensitive to wind, so try to operate the stove in a wind-sheltered area. Place the stove on a sturdy, level surface, as these setups can be somewhat precarious if the stove isn't well balanced. You can buy a fuel can stabilizer to help with this.

  

  A more heavy-duty stove option is the Coleman 533, if you can afford the extra weight and bulk in your pack. It can be used with white gas or regular gasoline, which makes this workhorse stove popular amongst overlanders and motorcyclists. The Coleman 533 has a much longer burn time than a typical 100g isobutane canister.

  

  If you don't want to carry a fuel canister, you could also consider a twig stove as long as you will be able to gather dry sticks and twigs as fuel.

Selecting the Right Method of Purification

The best method of purification will depend on the nature of your trip. There are multiple factors to consider:

• The nature of the water sources available on your trip. Are there fast-running streams and rivers? Or stagnant marshlands? The more stagnant or turbid your water sources will be, the more thorough your purification system should be.
• Your mode of transportation. Will you be on foot? Traveling via canoe? By bike? This will dictate how much you can carry with you, and should help you decide which type of system to choose.
• How remote is your trip? Is there nearby industrial activity that may add chemical pollutants to the water? Are there upstream cities?
• Will you you have the ability and time to make a fire for boiling water?
• How much will you value drinking cold water? If you're boiling, you'll need to allot time for your disinfected water to cool. You can cool boiled water by carefully placing the metal container in a lake or stream, being sure not to reinfect it with unsafe water.

The answers to these questions will help you decide on a water purification system that meets your needs. Enjoy your journey and stay safe!