WATER-CLOCK

Water-clock or clepsydra is a container that allows to measure a period of time by the regular flow of a liquid.

Unlike sundial or gnomon, the clepsydra allows, like the hourglass, to measure a period of time whether it is night or day.

There are some more complicated systems of the clepsydra which allow to measure a time lapse not by the flow but by the filling of a container(link).