HOW TO BUILD - AND USE! - A SOLAR STILL

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Now fill the reservoir, and to make sure that the still really works, add some salt to the water! After a few minutes the towel will begin to receive the liquid from the distribution tube. If it doesn't, or if the flow is too slow, very carefully open up the flattened tube in the bottom of the can with the point of an ice pick. Be cautious about this, however, as we don't want the water to flow into the towel faster than it can be evaporated.

Heat from the sun is trapped in the box, and the black towel absorbs this. Water is therefore evaporated from the towel much faster than it would be normally. The vapor, free of all solids, recondenses on the smooth surface of the glass and the foil on the back and sides. You'll see this a few minutes after you put in the water; first the glass steams up, then droplets form and run down to the bottom.

Don't expect the water to gush from the still like a Niagara, but put a can or bottle under the drain to catch the distilled fluid. On a sunny day the still will begin producing soon after you set it in operation and will drip water steadily into the container. To guard against evaporation of this distilled water, some experimenters run a tube from the drain to a corked bottle.

At first you'll probably reposition the still every half hour or so for greatest efficiency. When the novelty wears off, however, you'll likely decide on a compromise tilt—your latitude plus 10 degrees or so—and aim the collector south (unless you live below the Equator, of course).

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