To make a below ground still, you need a digging tool, a container, a clear plastic sheet, a drinking tube, and a rock
Select a site where you believe the soil will contain moisture (such as a dry stream bed or a low spot where rainwater has collected). The soil at this site should be easy to dig, and sunlight must hit the site most of the day.
To construct the still, you should—
You can drink water without disturbing the still by using the tube as a straw. By opening the still, you release the moist, warm air that has accumulated.
You may want to use plants in the hole as a moisture source. If so, dig out additional soil from the sides of the hole to form a slope on which to place the plants. Then proceed as above.
If polluted water is your only moisture source, dig a small trough outside the hole about 25 centimeters (10 inches) from the still’s lip . Dig the trough about 25 centimeters (10 inches) deep and 8 centimeters (3 inches) wide. Pour the polluted water in the trough. Be sure you do not spill any polluted water around the rim of the hole where the plastic sheet touches the soil. The trough holds the polluted water and the soil filters it as the still draws it. The water then condenses on the plastic and drains into the container. This process works extremely well when your only water source is salt water.
You will need at least three stills to meet your individual daily water intake needs. In comparison to the belowground still and the water transpiration bag still, the vegetation bag produces the best yield of water.