Cisterns are underground rooms for the storage of water and are part of any water system since ancient times. The name originates from the Greek κίστη kistē, which means basket. The word was used in Latin as cista meaning box and as cisterna which is a big box to store water. The word cistern is used in many languages. Cisterns are quite important in the middle east, and Arabic countries use the name آب انبار (Ab Anbar).
A cistern is underground because sunlight and warmth would cause the growth of algae and bacteria. Without light any photosynthesis is impossible. Also the heat might cause evaporation, underground it is cool and humidity might condensate at the ceiling and drip back into the cistern.
There must be an inflow from springs or rainwater from the surface or from roofs. Also there must be an outflow into a channel or water pipe. This makes the location of the cistern quite important, an optimal system works with water flowing continually downhill. Modern systems replace gravitation sometimes with pumps, but they cost money, may fail, and need energy to work. Modern water systems have a cistern on a hill or on a water tower, so the gravitation produces a continual pressure on the pipes. They are refilled with pumps, which work only for short periods.
There are millions of cisterns all over the world. They are pretty common and most of them are quite dull. But some are exceptional, huge chambers with row after row of columns, sometimes even with architectural specialties or artworks. Sometimes such cisterns are opened for the public, as museum about water works, as art gallery or for concerts. That's the kind of cistern we list on showcaves.com.