Solar Stills - Using the Sun to Purify Water
A solar still is a low-tech way of distilling water, powered by the heat of the sun. There are two basic types of solar stills: a box and a pit. In a solar still, impure water is contained outside the collector, where is it evaporated by sunlight shining through clear plastic. The pure water vapor condenses on the cool inside plastic surface and drips down off the weighted low point, where it is collected and removed.
To put it in easy to understand terms:
- 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 taste of the drinking water produced, solar stills have proven their worth in both survival situations and disaster relief zones where water is polluted. 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 or Landfall. 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.