Many of us take clean drinking water for granted, because getting a glass of pure water is usually as simple as turning on the faucet. In developing countries or in survival situations, however, fresh, clean water is a luxury. Solar distillation is a means of converting contaminated or brackish water into potable water. According to the World Health Organization, nearly 1 billion people lack access to safe drinking water; 2 million people die every year from diarrhea, many from unsafe water (see References 4).
History of Solar Distillation
Solar distillation is an ancient way of purifying water and making saltwater potable; Aristotle described the process as early as the 4th century BC. The first modern, large-scale solar still, built in Chile in 1872, consisted of 64 basins that supplied up to 20,000 liters of water per day to a mining community in the area. (See References 2, pages 1-2) The first mass-production of solar stills, by the U.S. Navy during World War II, created 200,000 inflatable stills for placement aboard the Navy's lifeboats (see References 1).
The Solar Distillation Process
The solar distillation process produces potable water much the way that nature produces rain. The sun's heat causes water to evaporate, separating the water vapor from salt or impurities. This water vapor condenses on the still for collection for use. (See References 1)
Single-basin Solar Still
Although types of solar sill designs vary, one proven design for field use is the single-basin. It features a basin covered by a sloped sheet of glass or plastic to hold polluted water; black basins better absorb the sun's energy. Glass-covered stills generally experience greater longevity, while plastic may be better for temporary or portable installations. The sloped glass or plastic allows the water to drain out of the solar still into a trough or tube. The output of clean water from a solar still is greatest in the evening, when the water within the basin is still warm, but the outside ambient temperature is cooling. (See References 1)
In a survival situation, make an emergency still with a need a few simple materials (see References 1). The U.S. Department of Energy describes a design for demonstration purposes using a mixing bowl as the basin. Add a couple of inches of salty water to the bottom of the bowl, and then place an empty cup in the center of the bowl. Cover the bowl tightly with plastic, placing a rubber band around the edge of the bowl to hold the plastic wrap in place. Drop a pebble or weight into the center of the plastic wrap, so it forms a cone shape above the cup. Place in sunlight where the water will evaporate, condense on the plastic wrap and drip into the cup. (See References 3)
Practical Uses for Solar-distilled Water
Solar distillation not only provides drinking water; the distilled water can meet other basic human needs, too, such as cooking, bathing and washing. When used to distill seawater, solar stills can reduce dependence on rainfall by providing a steady supply of water during drought. (See References 2, pages 2 and 3)
- The Shumacher Centre for Technology and Development: Solar Distillation -- Technical Brief
- Understanding Solar Stills; Joel Gordes, et al.; 1985
- U.S. Department of Energy: Rain Machine -- Solar Still
- World Health Organization: Water Sanitation and Health (WSH): Facts and Figures on Water Quality and Health
Based in the Midwest, Bethany Wieman has been writing articles about gardening, DIY, finance, travel and sustainability for more than 10 years. She was featured in the book "The Complete Guide to Growing Vegetables, Flowers, and Herbs from Containers." Wieman's professional background is in marketing, working with such brands as Swiss Army, Timberland and Callaway Golf. She holds a Bachelor of Arts in English.