A Quick look at Solar Stills
- last updated November 21, 2008
The elementary-school water cycle teaches children that there's a certain fixed amount of water in the world, and it goes round in a never-ending chain from organism to organism. You might have in your body, for example, water that once passed through Genghis Khan's mighty bladder. It is an arresting thought, if somewhat unwelcome when thirsty.
The premise behind the water cycle - water is evaporated, then comes down again as rain - is the crux of water-purifying solar still technology. In its most basic form, a solar still is made up of a cup, a sheet of plastic or some other transparent surface, and a bowl (or if you're stuck for bowls, a hole in the ground will do). The survival manual goes roughly like this:
- You fill the cup with the water you want to purify, put it in the bowl and cover it with the plastic sheet.
- You stick the apparatus out in the sun and the water evaporates, leaving the residue and dirty stuff in the cup.
- Once you cool it down again (by putting the apparatus in the shade, let's say), the water condenses and fills up the bowl, ready for consumption.
- Drink and enjoy the gritty, slightly alkaline taste!
Despite the rather dodgy (I love that word) taste of the drinking water produced, solar stills have proven their worth in both survival situations and disaster relief zones where water is polluted (most recently Hurricane Katrina). Before you go digging a hole next time you're stranded in the desert, however, keep in mind that what you lose in sweat while making a solar still can outstrip the water gains the still provides.
Solar stills can be purchased commercially from companies like Solaqua (http://www.solaqua.com/) or Landfall (http://www.landfallnavigation.com/memss.html). These usually cost a few hundred dollars if they comply with the relevant safety standards and protocols - it's often worth the extra money for a well-tested product. And the taste of the water is good, as the water is completely purified. Having said that, the concept of the solar still is simple enough to recreate in the field, and provides a cheap and energy-efficient way to recycle water on the go. And the water is safe to drink, despite any squeamishness over the technology's "what comes out must go in" approach.