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How to Purify Your Drinking Water with Solar Technology

Not only can you build a solar water-purification system, you can also design it. Designing is just as much fun as building, and it's more rewarding because the system's entirely yours. The system shown here uses distillation, a process that can remove salts, microorganisms, and even chemicals such as arsenic, leaving you with pure H2O. Here's how it works: If you leave salty or contaminated water in an open container, the water evaporates and leaves the contaminants behind. If you heat the water, the process speeds up considerably.

After the water evaporates, the water vapor condenses on the glass window and drips down into the catch trough. Tilt the catch trough just slightly and put a bottle or other container underneath the low end, and voila! Purified water.

You can make a purification system as cheaply or as expensively as you want. People in Third World countries use large, efficient versions of this same exact device that are capable of purifying hundreds of gallons a day. A system the size of a microwave oven can yield up to 3 gallons of purified water on a sunny day. Here's what you need for a basic solar still:

  • A wooden (or even better, sheet metal) enclosure; if you want to get imaginative, find a good metal box and cut a hole for the glaze cover

  • Reflective material such as aluminum foil (shiny side out)

  • Black paint (the kind used for barbeque pits works best)

  • Glass (you don't need glazed glass; you can get pieces of discarded glass from window shops for little more than a smile)

  • Insulation (the white foam stuff is cheap, effective, and easy to work with)

  • Glue (silicon sealant or similar weather-resistant material)

  • A tray that's black or has some other quality that absorbs heat

    A cross-section of a solar still, or water purification system.
    A cross-section of a solar still, or water purification system.

Now take a look at the assembly:

  1. Paint the exterior of the box black to enhance absorption.

  2. Install the reflective surface at the back and side walls of the enclosure and glue the insulation to the bottom.

  3. Put a tray of contaminated water inside the enclosure, place the glass on top, and aim toward the sun.

The first few times you use this device, the water may taste a little odd. Let the system "sweat" for a few weeks, and the bad taste will go away.

When designing or improving your unit, make filling the inner tray with water convenient. Position it by a hose, for example. Then you don't have to carry water to your system. Configure some kind of funnel through the sidewall so you can pour the water right into the tray without spilling. Make the unit so you can remove the glazing top and clean out the tray because the contaminants are going to remain behind. You'll get a good idea of how bad your tap water is when you see what's left.

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