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What is a Water Clock?

Mary McMahon
Updated May 23, 2024
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A water clock is a timekeeping device that uses a flow of water to measure time. It is not as accurate as most modern time-keeping devices, but when these clocks were first developed, they were quite adequate for the times. It is believed that they may be among the oldest of devices used to keep time, since written accounts of them date to around 4000 BCE, with physical examples from Egypt dating to 1500 BCE.

There are a number of ways in which a water clock can work, but generally, such clocks are classified as either inflow, or outflow. An outflow clock keeps time by allowing water to slowly drain away; an example from antiquity was a bowl marked with lines which had a small hole in the bottom. The bowl was filled and allowed to drain slowly, and the lines were used to keep track of time. In the case of an inflow clock, the flow of water into a container such as a cylinder is used to gauge the passage of time.

Water clocks may have originally been developed for the purpose of making astrological observations, when the passage of time can become an important factor. They were also apparently used to measure the passage of time during speeches and other events. The origins of this technology are not known, although Egypt appears to have some of the oldest examples; they were also used in Asia, the Middle East, and Greece, where the clock was known as a clepsydra, or “water stealer.”

A clock's accuracy could be fine tuned by pressurizing the water, or using various tools to alter the rate of flow. Some became quite sophisticated, turning into elaborate clock towers. As other timekeeping devices arose, the technology began to be displaced, and water clocks today are largely a curiosity, rather than a usable time piece, thanks to the fact that more precise methods of measuring time have been developed.

The need for more accurate time pieces began to emerge during the age of exploration, when mariners urgently needed accurate clocks so that they could measure longitude. During this era, more precise and reliable clocks began to be developed, and with the rise of the Industrial Revolution, when the need to keep accurate time became even more important, even better clocks were developed. By the 19th century, the water clock had been largely phased out, although they continued to be used in some remote areas where the rhythms of people's days did not need to be so precisely regulated.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a Historical Index researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments

By ronburg44 — On Dec 18, 2010

With the Egyptians massive use of technology and incredibly advanced technical know-how, there is no doubt in my mind that they were the first to develop these water clocks. It's interesting to me that archaeologists have in fact physical forms of these water clocks in their archives.

These amazing people, the same ones that built the incredible pyramids, must have had a meticulous insight into the inner workings of mechanics to be able to not only create feats such as large buildings in perfect form but also to control the flow of water at such an accurate rate that you could use it to tell time.

By fitness234 — On Dec 16, 2010

From a scientific point of view I have to wonder just how much the actual condition and quality of the water would affect the ability for a water clock to keep time, things like specific gravity, pH balance, as well as dissolved solids could make a difference in the way of the water flows in a water clock.

At the end of the day you just have to wonder truly how efficient and effective the use of water to keep time really is. Especially in our day and age of digital clocks and the ability to track the passage of time using atomic signals on the internet by means of atomic carbon decay, I think that the synchronization of clocks around the world has overcome the need for individual timepieces.

By CoffeeJim — On Dec 14, 2010

I think it is absolutely intriguing the many ways that humans have developed and devised different systems for timekeeping. From sundials to pendulums and even hour glasses, the human mind has always wanted to be able to keep track of the passage of time. It's almost as if it is in our innate nature to be able to determine what our or time of the day it is.

I think it's obvious to most humans that we do have a built-in rhythm. To scientists, this rhythm is known as your circadian cycle. While used by our body to keep track of our sleep cycle, this is just one form of how our biology actually is a ticking clock.

I've never heard of the water clock before but it comes as no surprise to me that there are many different types of clocks in this world.

By sherlock87 — On Nov 13, 2010

In a world where, as Douglas Adams once put it, "people still think digital watches are a neat idea", I find the idea of a water powered clock really interesting. It's always nice to think that while modern people think that we're doing things better than they've ever been done, a lot of the stuff we use has been around in some fashion for centuries, if not millennia.

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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