Water Thermometer

Water Thermometer

Watch the temperature rise with this homemade thermometer.

Is it possible to make a thermometer out of water? Absolutely! The best part about our Water Thermometer experiment is that you have all the materials you need in your own home. That’s right, you’ll be measuring temperature with this amazing homemade tool in no time.

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Experiment Materials

  • Glass bottle
  • Straw
  • Modeling clay
  • Food coloring
  • Container of hot water
  • Container of cold water
  • Heavy glove

Experiment Videos



Add a few drops of food coloring to the bottle. You pick the color!

Water Thermometer - Step 2


Fill the glass bottle up to the bottom of its neck with cold water.

Water Thermometer - Step 3


Place a straw (make sure it’s long enough) into the bottle. Pack clay around the straw and bottle neck so that the straw is centered in the bottle. Make as tight of a seal as possible.

Water Thermometer - Step 4


Now that you’ve made your thermometer, set the bottom of the bottle into the container of hot water.


Make sure you are wearing a heavy glove and remove your water thermometer from the hot water.


Put the water thermometer into the container of cold water.

How Does It Work

Water, like all substances, is comprised of molecules. In water, an individual molecule has the chemical formula H2O, dihydrogen monoxide. When water molecules are heated, their bonds stretch out and expand. In the Water Thermometer experiment, you’ve created a sealed environment around the water. That is to say, there is nowhere for the water to go as it expands because the rest of the space is filled with air. The straw gives the expanding water an area where it can expand, thus it rises up the straw.

In comparison, the opposite happens when water is cooled. The molecular bonds that hold the H2O molecules together contract, bringing the molecules closer together. Just as the water level in the straw rises when the water is heated, it lowers when the water is cooled.

Take It Further

Continue to experiment with different water temperatures and observe the changes in the water level of the straw.  Is there a maximum temperature where the water stops rising?

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