Clepsydra, also called water clock, is ancient device for measuring time by the gradual flow of water. One form, used by the North American Indians and some African peoples, consisted of a small boat or floating vessel that shipped water through a hole until it sank.

How does a water clock work?

A water clock uses the flow of water to measure time. ... An inflow water clock works in basically the same way, except instead of flowing out of the container, the water is filling up the marked container. As the container fills, the observer can see where the water meets the lines and tell how much time has passed.

What is a water clock for kids?

From Academic Kids

A water clock or clepsydra is a device for measuring time by letting water regularly flow out of a container usually by a tiny aperture. Since the rate of flow of water is very difficult to control precisely, water clocks could never achieve high accuracy.