The Yazd Water Museum was opened in 2000 inside a 19th century house, and it features exhibits of water storage vessels and historical technologies related to water.

The water clock (fenjaan) was a big pot full of water and a bowl with small hole in the center. When the bowl become full of water, it would sink into the pot, and the manager would empty the bowl and again put it on the top of the water in the pot. He would record the number of times the bowl sank by putting small stones into a jar.
The use of water clocks in Iran dates back to 500 BC. Later they were also used to determine the exact holy days of pre-Islamic religions, such as the Yaldā (winter solstice), Tiregān (mid-summer) or Nowruz (spring equinox) - the shortest, longest, and equal-length days and nights of the years. The water clocks used in Iran were one of the most practical ancient tools for timing the yearly calendar.
Persian water clocks were a practical and useful tool for the qanat's shareholders to calculate the length of time they could divert water to their farms. The qanat (a series of well-like vertical shafts, connected by gently sloping tunnels) was the only water source for agriculture and irrigation, so that a just and fair water distribution was very important.