Water for Backcountry Camping: How to Find It and Make It Safe to Drink

Why clear water isn’t enough

A creek tumbling between granite boulders, water so clear you could count the pebbles on the bottom: the urge to dunk your bottle right in is instant. Give it a second thought. Germs from human and animal feces wash into lakes, rivers, and streams, and water that carries them can look perfectly clean. The CDC, the nation’s public health agency, puts it bluntly: drinking straight from a clear mountain stream usually isn’t safe [1].

Three families of germs are to blame: bacteria, viruses, and microscopic parasites like GiardiaA microscopic intestinal parasite, spread through water contaminated with feces. and CryptosporidiumAnother microscopic intestinal parasite, and one that chlorine kills poorly.. They differ in size and toughness, and that’s what makes the choice of method matter: only some treatments handle all three, boiling first among them [1]. Children, pregnant women, adults 65 and older, and people with weakened immune systems are most at risk [1].

Finding a good water source

Treatment starts before you ever fill your bottle, with where you get your water. A few simple rules head off most nasty surprises:

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• Find water sources on the map before you head out: springs, creeks, lakes. By late summer, a creek marked on the map may have dried up.
• Check what’s upstream: grazing cattle, a hut, homes, a road, farm fields. Germs come from human and animal feces [1].
• Go for clear water: let cloudy water settle, then strain it through a clean cloth before you treat it, because particles interfere with disinfection and UV light [1, 2].
• Avoid water that might be chemically polluted: an odd smell, an oily sheen, foam, an abandoned mine, an industrial discharge. Neither boiling nor disinfection makes water contaminated with chemicals, toxins, or radioactive material safe: find another source [1].
• Watch out for algal blooms: discolored or foul-smelling water, foam, scum, mats of algae, or paint-like streaks on the surface point to an algal bloom, often of cyanobacteria (blue-green algae), which can produce toxins [3]. No filter or other treatment device designed for the backcountry removes or destroys these toxins, and boiling doesn’t get rid of them either: it can even concentrate them [3, 4]. Since they’re sometimes present with no visible sign at all, also follow any posted advisories; if you see a bloom, find another source [3, 4].
• At a hut or campground, read the sign by the spigot: the water may be marked non-potable.

Boiling: the gold standard

Boiling kills every type of germ, including viruses, bacteria, and parasites [1]. On how long to boil, two health authorities don’t quite agree. The World Health Organization says bringing water to a rolling boilBig bubbles rising nonstop, even when you stir the water. is enough: bacteria, viruses, and parasites are inactivated below 212 °F (100 °C), and Cryptosporidium in under a minute above 158 °F (70 °C) [2]. The CDC says to keep it at a rolling boil for 1 minute, and for 3 minutes above 6,500 feet (about 2,000 m) [1].

I’d go with the more cautious advice, the CDC’s: it costs a little extra fuel and leaves no room for doubt. According to the WHO, boiling still works at high elevation and even in cloudy water; its downsides are the fuel it burns and the lack of any residual protection once the water cools [2]. Let it cool naturally, without adding ice, and protect it from getting contaminated again [2], say, in a clean, covered container.

Filtering: what a filter catches and what slips through

A filter stops anything bigger than its pores. So it all comes down to the stated pore size, as long as it’s absoluteThe maximum pore size, guaranteed by the manufacturer: nothing bigger gets through. A “nominal” size only catches some of the particles that size. [1]:

• 1 micron or smaller, or NSF 53 or 58 certification for cyst reduction: the filter stops parasites, but not viruses or all bacteria;
• 0.3 micron or smaller: it stops parasites and bacteria, but not viruses;
• reverse osmosis stops parasites, bacteria, and viruses, and even salt [1].

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When you pick a filter, aim for 0.2 micron absolute or smaller: the CDC’s guide for travelers puts the pore size needed to stop gut bacteria at 0.2 to 0.4 micron [5], and the Minnesota Department of Health rates filters of 0.3 micron absolute or smaller as only moderately effective against bacteria [4]. Some hollow-fiber filters go down to 0.1 micron, like Sawyer’s [6]. Only ultrafilters, with 0.01-micron pores, also stop viruses; portable versions exist, but they cost more and filter more slowly [5].

Viruses are too small for most backpacking filters. That’s why, when you can’t boil, the CDC recommends filtering the water and then disinfecting it [1]. When you fill up and when you filter, keep the clean side away from untreated water: not a drop should reach your bottle of treated water, its mouth, its threads, or its cap, or the filter outlet, or the water can get contaminated again [2, 8].

Disinfecting: tablets and drops

Chemical disinfectants kill bacteria and viruses, but not always parasites [1]. Chlorine and iodine don’t work well against them. Chlorine dioxide kills Giardia and can also handle Cryptosporidium, but slowly: it needs a contact time of several hours, according to the CDC’s guide for travelers [5], and the label for Micropur MP1 tablets requires a 4-hour treatment time [11]. Water you drink after half an hour isn’t protected against this parasite. Filtering the water first is still the safest bet [1], and the product’s instructions set the dose and the contact time [1]: if they list different times for different germs, go with the longest.

Iodine calls for one more precaution: the CDC advises against it for pregnant women, people with thyroid problems or an iodine sensitivity, and anyone using it for more than a few weeks at a time [1].

UV light: effective, with one catch

A portable UV light kills parasites, bacteria, and viruses in small amounts of clear water [1]. Here’s the catch: in cloudy water, particles shield germs from the light. So filter the water before you treat it with UV [1]. And bring a way to recharge the device.

Which method for which trip?

• A stove in your pack and time to spare: boiling, which kills every type of germ [1, 2].
• Going light, with clear water: a filter rated 0.2 micron absolute or smaller, then a disinfectant, since viruses get through the filter [1, 5].
• Cloudy water: let it settle, strain it through a cloth, then treat it [1, 2].
• Water you suspect is chemically polluted, or that has an algal bloom: neither boiling nor disinfection is enough; find another source [1, 4].

A sip of cold creek water is one of the simple joys of a backcountry trip. Treated, it’s every bit as fresh, and so are you the next morning.

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Worth watching

REI shows what to look for in a water source and the right way to collect water before you filter it, the hands-on side of choosing a good source.

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Guillaume Hoarau

Camping, backpacking, bushcraft and hiking

Guillaume Hoarau writes for Outfarer about camping, backpacking, bushcraft, and hiking. A survival-skills buff and a collector of vintage field manuals, he loves clear explanations, lists that actually help and other people’s stories, which he tells well.

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