Over 97.5 percent of the earth’s water contains salt, and desalination is the process of removing salt from water. More than 16 billion gallons of desalinated water are produced daily, with much of it designated for drinking water in the Persian Gulf countries. It is a challenge for engineers worldwide to find a desalination process that is cheap enough to bring desalinated water to the poor and remote regions of the earth.
Currently there are several techniques used for the desalinating water in large quantities, including forward osmosis, carbon nanotubes, and biomimetics. Evaporation desalination, however, is still the most commonly used. All desalination processes produce dangerous by-products, such as concentrated brine, that pose environmental hazards to fresh water and animals. You may want to learn how to desalinate water on a smaller scale for a variety of reasons, which may include to teach students if you are a teacher or to help you if you’re lost at sea. One evaporation desalination technique (or solar water still) that requires little in the way of supplies and may be used in a variety of settings is examined below.
Fill a large bowl or other large container with salt water. If you are without bowls or buckets, you may need to dig a shallow depression and line it with plastic or leaves to prevent the water from seeping out.
Place a smaller container in the center of the larger bowl.
Place a piece of plastic over the large container. The plastic should be large enough that you can tie it down and that the plastic can sag a little. If you are using a bowl, use a rubber band or string to keep the plastic in place. If you have dug a hole, use rocks to hold down the plastic.
Place a small rock or marble in the center of the plastic cover, directly over the smaller container. Allow the plastic to sag a little so it is pointed to the center of the smaller container.
Set the water still in a sunny location for a few hours. The sun will cause the water to evaporate, and it will try to rise as steam. It will condense on the plastic covering and leave the salt behind in the larger container. The condensation will form as drops on the plastic and naturally roll towards the smaller container, eventually falling into it.
Remove the plastic covering after a few hours, and remove the smaller container. This will contain the purified water.
Dispose of the remaining salt water carefully. It is highly concentrated and may cause damage to plants or animals.