How to Make a Water Clock

When I explained to my eight year old son that ancient peoples didn't have clocks like we do today, he was surprised. I don't think the thought had ever occurred to him that without batteries or electricity, the hands of a clock simply couldn't move.

In Ancient Greece, they used a water clock to time short events. It was called a clepsydra (KLEP-sye-druh). I thought it would be fun to make our own version of these ancient clocks.

What You Need

masking tape

fine-tip permanent marker

two of the same empty plastic beverage bottles

thumbtack

pitcher of water

timer (we used a stopwatch app on the iPad)

craft knife (to be used by an adult only)

funnel to make pouring easier

How to Make It

Remove the labels from the beverage bottles for clear viewing to the inside.

An adult should cut one of the tops off the bottle with a craft knife. Recycle the top; you won't need it. With the top cut off, the bottom of the other bottle should fit snuggly down into it. Label the bottles if you'd like (bottle A is the complete bottle and bottle B is the one you've cut).

Turn the complete bottle over (bottle A) and put a thumbtack through the center of the bottom of the bottle to make a small hole. (This is the hardest part of the whole project.)

Mark on this bottle where the full line is (figure this out by nesting bottle A inside the bottle B; the distance from the bottom of bottle B up to the bottom of bottle A or slightly below is where you should draw the line on bottle A). Note: We botched this up but it's important to know how full to fill your bottle each time. You'll want to be consistent.

Grab a length of masking tape and adhere it vertically to the side of the cut bottle (bottle B).

Now get your timer and the pitcher of water ready. Pour the water, using a funnel if desired, into the neck of bottle A (your bottles should be nested) and immediately start the timer. Pour up to the fill line on bottle A.

When one minute passes, make a small mark at the water line on the masking tape on bottle B. Continue to mark the minutes until the water has completely emptied from the top bottle into the bottom one. We only marked the first 10 minutes, but you can mark as many minutes as you'd like.

Now you can dump out the water and put the timer aside. Another pour of the pitcher and you can calculate how long something takes with just your water clock!

This great activity was adapted from instructions in the book Spend the Day in Ancient Greece.