The oldest water clock of which there is physical evidence dates to ca. 1391-1353 BC, during the reign of Amenhotep III where it was used in the Temple of Amen-Re at Karnak.
This alabaster water clock has 12 carved columns of 11 false holes, corresponding to the hours of the night. The water flowed through a very small hole made in the center of the bottom, emerging on the outside under the figure of a seated baboon. To know the time, one had to look inside the basin to observe the water level and read the time according to the nearest false hole.
The outside surface of this clepsydra, or water clock, is decorated with figures and text that show symbols of certain planets and constellations and give a list of the protective spirits for each of the ten days of the ancient Egyptian week. The middle register, or section, is occupied by the circumpolar stars under the aspects of various gods and animals.
New Kingdom, 18th Dynasty, reign of Amenhotep III, ca. 1391-1353 BC. Now in the Egyptian Museum, Cairo. JE 37525