How do you tell time? Nowadays, many people look at a phone or smart watch to see what time it is. Others might still consult a wall clock or old-fashioned wrist watch for the hour. But clocks seem to be everywhere--in our cars, on the stovetop, on our computer screens. Yes, people really like to tell time!

Have you ever WONDERed how people measured time before clocks? You might think of the sundial. But for a sundial to work, you need... well, the sun. What if it was a cloudy day? Or night time? How did they measure time then? To solve this problem, many cultures built water clocks. 

You may be familiar with clocks that go tick-tock-tick-tock. Water clocks, also called clepsydras, sound more like drip-drip-drip-drip. That’s because they relied on flowing water to measure the hours of the day. 

How did water clocks work? Cultures designed them in a few ways. The oldest record of the devices is from Egypt in the 14th-century B.C.E. However, some experts believe the Babylonians taught the Egyptians how to build the clocks.

The earliest water clocks came in two types: inflow and outflow. Both designs involved two large containers. One container was filled with liquid and suspended over the second one. Water dripped through a hole in the bottom of the filled container to the bottom one. 

On inflow water clocks, the bottom container was marked with the hours of the day. People could tell the time by how full the container became. For outflow clocks, it was just the opposite. The time was marked on the top container. To tell what hour it was, people looked at how much water had drained from the container.

Water clocks quickly became popular in other parts of the world. As they spread, they also evolved. The ancient Greeks built many of these devices, as did the Romans. Both of these cultures made clocks that used gears and depended on water pressure. They also added bells to sound at assigned times and other mechanical features that made the clocks much more complex. The Romans used these  to set time limits for people speaking in court. When the water ran out, so did your time!

Across ancient Asia, people built water clock towers. One built in China in 1088 C.E. was 30 feet tall! In North America, American Indian nations built devices  that used small floating boats that sank over the course of the day. 

Can you still see water clocks today? Of course! Many of them use water as a power source to turn gears. Though they tell time, most are pieces of kinetic art. One such popular attraction is the Hornsby Water Clock in Australia. If you visit the Indianapolis Children’s Museum in America, you could also check out the “Time Flow Clock” by Bernard Gitton. 

Have you ever seen a water clock? What other interesting ways do you know of to tell time? Do you use an alarm clock at home? How about an hourglass? Over the centuries, people have come up with a variety of ways to measure time!