An underground water storage tank, typically called a water cistern, is used to safely store potable drinking water underground. Underground water storage tanks can hold thousands of gallons of water for agriculture or a few hundred gallons to support the water needs of a small home. Cisterns are popular water storage tanks around the globe, and most commonly seen outside of the United States. Water cisterns are usually made from ribbed plastic resin. The ribbing allows the storage tank to be buried underground without disrupting the soil. It’s important for water cisterns to never be completely drained of water. The pressure from the earth could warp the plastic resin and distort the tank. The water helps equalize the pressure between the tank and the surrounding soil.
In addition to drinking water, cisterns can also be used to store wastewater and rainwater. Rooftops can be equipped with rainwater collection troughs that harvest rainwater and channel it underground into a cistern. For people living in areas where groundwater is unsuitable for drinking and municipal water is unavailable, this is a very viable water source if rainfall is heavy enough. For example, mining towns along the Eastern seaboard of the United States have adopted cistern rainwater collection because of the damage done to local groundwater by mining. The rainwater can then be pumped into the home, like from a well, and used for bathing, cooking, and drinking (although it will first need to be passed through a water filtration system.)