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SOLAR STILL

A build-it-yourself solar distillery is one of the best ways to obtain drinking water in areas where the liquid is scarce. Developed by two doctors in the U.S. Department of Agriculture, it's an excellent water collection device. Unfortunately, you must carry the necessary equipment with you, since it's all but impossible to find natural substitutes. The only components required, though, are a 5' X 5' sheet of clear or slightly milky plastic, six feet of plastic tubing, and a container-perhaps a collapsible drinking cup-to catch the water. (You can, of course, fashion some sort of receptacle in the wilderness . . . from stone or wood.) These pieces of gear can be folded into a neat little pack and clipped onto your belt.

To construct a working still, use a sharp stick or rock to dig a hole four feet across and three feet deep. (Try to locate the excavation in a damp area, gully, or river basin to increase the water catcher's productivity.) Place your cup in the deepest part of the hole. Then lay the tube in place so that one end rests all the way in the cup and the rest of the line runs up-and outthe side of the pit.

Next, cover the hole with the plastic sheet . . . securing the edges of the material with dirt and weighting the sheet's center down with a rock. The plastic should now form a cone with 45°angled sides. The low point of the sheet must be centered directly over, and no more than three inches above, the cup.

The solar still works by creating a greenhouse under the plastic. Ground water evaporates and collects on the sheet until droplets form, run down the material, and fall off into the cup. When the container is full, you can suck the refreshment out through the tubing, and won't have to break down the still every time you need a drink.

A good solar still, located in a damp area, should keep collecting water for quite a few days. In drier regions, such as deserts, I recommend making the hole four feet deep and placing crushed herbaceous plants (cactus and thistle are good choices) in the pit to increase the still's output. I once used such a setup in Death Valley and was able to obtain a gallon of drinking water a day! Be careful to use only edible plants for such water boosters, of course, as many poisons will evaporate and drip down into your cup even more rapidly than will water.

For the same reason, I don't recommend using a solar still to treat chemically contaminated water. The device does an excellent job of purifying bacterially polluted water, though: Just pour the liquid onto the surface soil next to. the plastic covering. The water will then filter through the ground and be distilled into a quite safe drinking supply. In fact, using this technique, the solar still will even purify human urine!

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