Build a Water Timer (Student Instruction)

Design and build a timer that works by measuring how much water drips out of or into a container.   
Water engineer Allie Reiling demonstrates Water Timer activity



  • clear plastic and/or waterproof containers of assorted sizes and shapes
  • tape
  • something that can poke small holes in plastic cups and containers
  • stopwatch or clock with second hand
  • water
  • towels to mop up any spilled water
  • ways to make the two containers different heights, such as a bench or a table with books


How can you build a timer that measures 3 minutes consistently, using the movement of water from one container to another?

There are three constraints for this challenge (an engineering constraint is a limitation on your design):

  • Use only the materials provided (but no need to use them all).
  • The timer has to measure approximately the same amount of time – 2 times in a row.
  • The water has to stay inside the containers.

Brainstorm Designs

Spend a few minutes exploring the different materials. Think about how you might use them together.

  • Do you know about the flow rate of water? That’s the amount of water that comes out of a pipe or fixture within a certain period of time. To see what it looks like―take one of your containers, poke a small hole at the bottom of it, and plug the hole with a piece of tape. Now fill the plugged container about 1/3 full of water. When you’re ready, place the plugged container over a second container to catch the water and unplug it. What does the water flow look like?
  • What do you think will happen to the flow rate if you add more water? Or make a bigger hole? Try them both and compare what happens.
  • Now it’s time to experiment with different containers, heights, hole sizes, and amounts of water. Notice whether the flow of water is stronger or weaker depending on how much water is in the container, and if the flow changes as the water leaves the container. See whether you find it easier to measure water coming out of the top container or flowing into the bottom one.

Build and Test

  • Build your water timer based on your research.
  • When you are ready to test, get your stopwatch ready. Test your water timer once to see how close it gets to three minutes.
  • Test your timer a second time. Does it measure the same amount of time as the first test? How close did you get to three minutes?
  • If your timer measured more or less than three minutes, or if the time was different for each test, no worries. Engineers learn from what isn’t working all the time.

Evaluate and Redesign

What worked and what didn’t? Think about any changes you would like to make. Ask yourself:  

  • If the time it takes to empty the top container varies, what do you think is causing the difference? 
  • What is the weak point of your water timer? 
  • What happens if you change the angle of the top container? 

Make Changes and Try Again!

  • Try to make your timer even more accurate, to within 2 seconds. 
  • Or, figure out how to make simple changes to your timer so that it can measure 5 minutes accurately. 

Share Your Results with a Teacher, Parent/Guardian, or DiscoverE!

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