Klepshydra – Ancient Greek Water Clock




Introduction: Klepshydra – Ancient Greek Water Clock

About: graphic designer, composer, musician

This is one of the eldest methods for measuring time – in some cultures (Egypt, Greece, Persia, and more) it was developed – and is still in use – thousands of years ago. For my simple model (and at least also the original is not more than this but different materials) of ‘Klepshydra’ you should find everything needed in your household and it is easy to make in no time! This Klepshydra water clock can measure time of about 24 minutes – and this is approximately the time a speaker could maximal get in the world’s first democratic parliaments in Greece of ancient times. So, up from now you know why we are saying :-) »time is RUNNING OUT«!



  • pencil
  • cutter
  • glueing tape
  • lighter, no problem if you have none
  • pin
  • a clock – for calibrating, I used my iPad


  • PET bottle – I used one for sparkling mineral water, 1 l
  • paper
  • a glass – or an other volume; smaller is better, minimum: volume of PET bottle
  • water
  • a cup – used as stand for the bottle; this is only a nice option but not necessary
  • books – or something you can make a little tower

Step 1: Make a Paper Stripe for the Scale and Mount It

Just cut a stripe from the paper: length is almost the hight of your glass (receiving volume) x 1,5 in. Mount it vertically on glass with glueing tape; make sure you can later make a mark for the first minute near the bottom of the glass.

Step 2: Make a Mini Hole in PET Bottle

Best practise: Heat the pin above / in a lighter’s flame until the tip starts glowing – this makes it more easy to come through the often a bit thicker bottom of the PET bottle. But you can do it also without glowing the pin’s tin.

Step 3: Fill the PET Bottle, Build the Tower

Close the mini hole with one finger, fill the bottle with water, close the bottle cup and place it upside down in the cup. Build up a little tower of books or something else: at least a bit higher than your receiving volume. Make your calibrating clock (I used the iPad) ready to go.

Step 4: Start Calibrating

Place the receiving volume (glass flask) near the book tower, place the PET bottle on top of the book tower – make sure the mini hole is directed towards the receiving volume. Open the bottle cup – otherwise the water cannot come out of the bottle continuously – and open the mini hole by moving your finger away. And here we go! Images here are showing how it should look like after 15 and after 38 seconds …

Step 5: … Making the Scale

Start making the scale by doing a mark with the pencil on the paper stripe after the first minute at actual level of water in the bottle, make a mark every minute, number the minutes …

Step 6: Minute 19, Minute 20, …

… still running but we’re coming soon to an end – obviously …

Step 7: 24 Minutes – End of Calibrating

After a bit more than 24 minutes the 1 l water has completely done its way down to the receiving glass – »time was running out« so to say :-) I made every minute a mark on the paper stripe (almost, because of making photos) and so this is the final scale and the ‘Klepshydra’ water clock is now ready to measure time itself.

Step 8: Test Run – Does It Really Work? Yes!

I re-filled the PET bottle, made the receiving volume empty again and started the ‘time is running out’ process again. I was very curious how exactly this simple water clock will measure the time so I started also the clock on the iPad for being able to compare ‘Klepshydro’ water clock time with iPad time and how much the difference will be at the end. The result is amazing: There was visually no difference – that means: it is definitely much less than 1 minute. And this is – in my opinion – definitely accurate for this kind of clock! :-)

P.S. … just another note:
I think the Klepshydra water clock is cool for discussing ‘time’ with little children because you can definitely ‘see’ the time (water) is running and therefore time is nevermore such an abstract thing.

Also the Klepshydra water clock can be inspiring for philosophical thoughts: No time is lost, it is only changing its ‘state’: From up to down, one volume becomes empty, the other full – because of that …

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    Reply 2 years ago

    Thanks, for this input – I never heard before about Mariotte’s siphon! 😊


    2 years ago

    I learned something new. Thanks.


    2 years ago

    For older students, you could also bring in Torricelli's law (the water flows slower as the height of water in the upper container goes down). It might be easier to see this effect with cylinders. With your conical flask, the narrowing of the receiving container counteracts the slowing of the flow rate, so that the marks appear almost evenly spaced. A calculus level question would be what profile would give evenly spaced marks.


    Reply 2 years ago

    Hello, hello! Ah, I see, you go into details – this is great, thank you for your comment! :-) So, maybe you are interested what I found out because it did indeed some observations in details but could not pack it into Klepshydra’s instructable because I was so late with it for making a contest entry! ;-) It’s not so clear to see on the images but it is like this: START: The very fist minutes (till minute 8) the distance of the marks on the scale increase a bit –> difference of water pressure in upper bottle generates no visible effect but conical flask effects: (almost) same volume –> smaller flask diameter –> more distance between the marks. THEN – minute 8 to 16: falling water pressure and decreasing flask diameter are more or less in balance, so the marks in this section of equal distances; UP – from minute 16: water pressure becomes less and less but decreasing flask diameter is not able to compensate this anymore –> result: the distance of marks is now decreasing, according to the falling water pressure.

    A special note for ‘different distances of the marks’: All these increasing and decreasing of the mark’s distances are within a range of only 1 mm and I know my ‘scaling artwork’ looks and is not so accurate. But: since I’m working as a graphic design pro and being a little bit a ‘typographic nerd’, I usually adjust the heights of fonts (for example) in steps of ~ 1/40 mm or ~ 1/10 of a ‘typographic point’; so I am pretty sure I can interpret my own handwritten scale correctly while studying my own hieroglyphics. Thanks again for your inspiring comment, all the best from Austria! :-)