For millennia, humans have been using water as an energy source. There are early examples of hydropower, where energy could be created by attaching a paddlewheel to a device to harness the rotary power provided by the energy of flowing water. Millers have used this technique for thousands of years to refine grains. Other, more novel ideas have been used over the centuries to use the properties of water to advantage.
One of these ideas was in using water to create an accurate timepiece. At the time early water -powered devices were being developed, accurate time was not really much of a consideration and most time was told through the use of sundials. Much later a device was developed that used weight falling or a spring wound to store energy, with a mechanical regulator used to incrementally moderate the energy released into the gear mechanism so that some indicating mechanism could display the approximate time of day.
The attempt to use a liquid, specifically water, as a mechanism for creating a timepiece has fascinated experimenters through the centuries, with the oldest attempts occurring in China, nearly 4000 years ago. Water clocks, or more specifically, clepsydra (the Greek word for them), are timepieces that use the measured flow of water to indicate time, rather than taking power specifically from falling or flowing water. These devices were used throughout the ancient world, from China, to Babylon and Egypt, India, Greece, Europe, and Japan and Korea.
The simplest method for creating a water clock is by putting it in a cone-shaped vessel with marks inside the bowl, and a tiny hole bored in the bottom. As the water drains out of the vessel, the marks are uncovered, indicating the time. The vessel is cone-shaped since the pressure drops as the water gets near the bottom, and therefore the flow of water decreases out of the hole as the vessel drains.
This type of timepiece is not very accurate and was very difficult to calibrate. Additionally, as the water temperature changes, water viscosity also changes, making the accuracy of this device questionable and allowing only gross approximations of time, especially when the sun was nowhere to be seen on a sundial’s face on a cloudy day, or at night. Indeed, water clock calibrations were made with sundials and were used for millennia as the most accurate way of timekeeping that could be devised, until the mechanical pendulum was employed.
During Roman times, a mechanism was added to meter the flow of water such that accuracy improved, and many cultures around the globe experimented with this means of timekeeping, with some mechanisms becoming extremely complex. One of the most novel ways that water was used to keep time was through the use of the use of capillary water flow, and a successful time-flow clock was created in 1979 using a series of glass tubes and vessels with no moving parts. However, the clock was not very accurate because as the viscosity changed in the water as temperature changed. The accuracy of this clock varied considerably to as much as ± a half-hour change per day with only a single degree Celsius of temperature change.
Water oscillation (wave motion) has long been theorized as a possible energy source. Many attempts have been made to utilize this source of mechanical energy, even as far back as the mid-1800’s. From 1855 through 1973 there were 340 patents granted for water powered devices in the UK alone. In 1910, a device constructed by Bochaux-Praceique to light and power his house at Royan, near Bordeaux in France. It appears that this was the first oscillating water-column type of wave-energy device. Since then there have been many more practical devices, and in 2003 the first marine energy center to study this phenomenon was built in the U.K. Since then, many of the principles employed within the earliest water clocks have been used to harness this vastly untapped energy resource, and full-scale projects are currently underway to harness water power in ways that heretofore were not thought possible.
In the modern era, water is used to generate hydroelectric through hydroelectric dams, which provide a source of low-carbon energy. Electrolysis, the process of separating hydrogen and oxygen in water molecules, has also been studied as a way to provide low-carbon energy sources.