Techniques for getting water

When your supply runs out and there is no river at hand, these techniques give you extra water. Almost all of them produce little: use them to supplement, not as your main source. All water you get this way must be made safe to drink (see below), unless stated otherwise.

Collecting rain

It is the technique that gives the most water with the least effort. Every inch (2.5 cm) of rain on a square foot of surface equals about 0.6 gallons (2.3 L). By that calculation, a 2,000-square-foot roof collects about 1,000 gallons for every inch of rain. A 10 × 10 ft (3 × 3 m) tarp can collect dozens of gallons in a downpour.

1. Tarp: tie the four corners to posts, railings, or trees, with one corner lower (or a weight in the center and a low spot) to direct the water into a clean bucket.
2. Gutters and downspouts: put a bucket or a clean jug under the roof downspout.
3. Discard the first minutes of rain: they wash off dust, bird droppings, and dirt from the roof. Permanent systems use a "first-flush diverter" for this (CDC).
4. Always treat it before drinking. The CDC warns that rainwater is not necessarily safe: it carries germs from the roof and can carry chemicals from the roof, gutters, or pipes.

Transpiration bag

Plants draw water from the soil and "sweat" it through their leaves. If you enclose a living branch in a clear bag in the sun, that water condenses inside the bag (FM 21-76 technique).

1. Choose a tree or bush with lots of green leaves, in the sun, that you recognize as nonpoisonous (see chapter 6). If the plant is poisonous, the water can be too.
2. Put a small rock in a large clear plastic bag.
3. Cover a leafy branch with the bag and tie it tightly around the branch, near the opening, so the humid air does not escape.
4. Lower the tip of the branch (tie it downward if needed) so the bottom of the bag, with the rock, sits lower than the opening. The water collects there.
5. Remove the water without untying the bag: with a tube that reaches the low point, or by quickly opening and closing a hole at the bottom.
6. Change branches every few days; the same branch can be used for 3 to 5 days without permanent damage, according to the manual. Set up several bags at once.

The yield varies greatly with the plant, the sun, and the humidity: in general, little water. Try it knowing it is a supplement. If the plant is not poisonous, the water comes out fairly clean, but disinfect it if you can.

Collecting dew

1. Go out before dawn, when the grass and leaves are wet with dew.
2. Tie clean rags or bundles of fine grass around your ankles and walk through tall grass, or wipe an absorbent cloth over the leaves and over the tarp or the car cover.
3. Wring out the rag into a container and repeat. Treat the water.

Digging in a dry streambed

1. Look for the outside of a bend in the dry channel: it is where the water ran with the most force and where moisture stays the longest. Low points and places with green vegetation or damp sand also work.
2. Dig a hole during the cool hours. If the sand comes out increasingly damp, keep digging; if it stays dry, do not waste more sweat: try somewhere else.
3. Wait for the water to seep in and collect at the bottom. Scoop it out with a cup, let it settle, and treat it.

Water in the city

In the city there is plenty of water, but not all of it is fit to drink. From best to worst:

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