Leonardo da Vinci designed a water clock that used flowing water to drive its timing mechanisms.
Leonardo’s notebooks include plans for a water-powered clock and related hydraulic devices. In a water clock, the controlled movement of water can measure time by filling or emptying a vessel, raising a float, or driving linked mechanical parts. Leonardo studied these effects as part of his wider investigations into water flow and machines.
His clock designs were conceptual and experimental rather than evidence of a complete, continuously operating clock built by him. Water clocks themselves are far older than Leonardo, with examples known from ancient civilizations. Leonardo’s contribution was to develop and record ingenious mechanical arrangements that used hydraulic motion for timekeeping.
The device is not a pendulum clock: pendulum regulation became important much later, after Galileo’s studies and Christiaan Huygens’s 17th-century clockwork. It is also not a sundial, which indicates time from the position of a shadow rather than from moving water.