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Summer STEM: Build a Water Clock

Cover of Honest History Issue 4 and illustrations of making a water clock


We’re back with our final installment of our summer STEM series. This one comes straight from our kids magazine, Issue 4 | Story of an Empire. As summer comes to an end, it becomes all too clear that time is flying by. Is it back to school already? How did we lose track of time? 

Well this STEM activity is all about exactly that: time. 

Throughout history, humanity's quest to measure time has led to remarkable inventions and innovations. Ancient civilizations relied on the natural world, like the position of the sun, moon, and stars to track the passage of time. You may have heard of a sundial, which tells you what time it is depending on where the Sun casts its shadow. But have you heard of clepsydra? This is another ancient time-keeping device, and it is a great way for kids to explore the concept of time.

In Greek, clepsydra roughly translates to “water thief.” This is a fitting name for a clock that, you guessed it, uses water to measure time.


Honest History Magazine Issue 4 with a water bottle, pen, and scissors

What You’ll Need:

  • A plastic water bottle
  • A bottle cap
  • Scissors
  • A timer (you can use a phone)
  • An awl or other pointy object to make a very small hole 
  • Permanent marker

Cut the water bottle into two parts. Using scissors, cut the water bottle into two pieces. The top part should be smaller than the bottom part.

Make a small hole in the bottle cap. Take the awl or other sharp tool to make a very small hole in the top of the bottle cap. 

Screw the bottle cap onto the top of the bottle and flip it over. You want to place the top of the bottle inside the lower part. There should be several inches of space between the bottle cap and the bottom of the bottle. 


Plastic water bottle cut in half


Pour in the water and time it! With your timer ready, pour water into the top portion of the bottle and time how many drops fall in one minute. You can add dye to your water to make it easier to see. 

Mark it. After one minute, take your marker. Draw a line on the lower half of the bottle to mark where the water level is. Then, mark where the water is at two, three, four, and five minutes.


Plastic water bottle with marked water level


Your clock is ready! Once you’ve marked the water levels up to five minutes, you are now ready to use your water clock. See if you can clean your room in five minutes or how fast you can count in one minute using your cool new timer.


You can imagine how this might work if the clepsydra were much bigger. Thousands of years ago, Greeks and Romans were able to make water clocks that measured multiple hours during the day. It’s amazing to think just how ancient this time-keeping device is. 


Water clock from 3rd century BCE

19th-century drawing of an ancient clepsydra from the 3rd century BCE. Image credit: Wikimedia.


We hope this activity helps fill these last few days of summer.
 Want to try some other STEM activities, read our previous blog posts here: Build a World War II Plane and Become a Map Master. And don’t forget to check out Issue 4 | Story of Empire to learn about other ancient Roman innovations.