Water: Classroom presentation

In today's lesson we're going to investigate the water that comes out of our taps, and discover whether warm water can sometimes freeze quicker than cool water.

We'll develop our investigative skills and gather evidence through doing things, and taking note of what happens. We'll discover that all results are valid, even if unexpected!

This investigation links to the Materials and their Properties element of the curriculum.

Introduction to the water investigation

We asked "The BFG" star Ruby Barnhill to investigate water for us, watch this short film to find out what she discovered.

Prepare your equipment

Your teacher will split you into groups for the investigation. Each group will need: two mini cups per person, some plastic trays and a marker pen.

Follow these steps:

  1. Mark a line on your mini cups to show 25ml (your teacher will show you how)

  2. Mark half of your mini cups with a C for cool water and the other half with a W for warm water

  3. Take turns to fill the mini cups marked C with cool water

  4. Your teacher will fill the W cups with warm water for you

  5. Ask your teacher to put all the mini cups in the freezer.

Take turns to fill your C cups to the line with cool water

Test your water hardness

While you are waiting for the water to start to freeze you can test the hardness of the water from your tap. Your teacher will give you a water hardness testing kit which includes some testing strips and a colour chart.

• Place one strip in a mini cup of cool water and keep it there for 2 seconds

• Shake off the water

• Wait for 10 seconds

• Your stick will change colour! Compare the colour to the colour chart and note down the number next to the colour which matches your stick.

What do the colours mean?

The colours on the chart show how hard your water is. 1 is soft water and 5 is hard water. Make sure you note down the hardness of your water.

Hold the test strips in the cool water for 2 seconds

Start the experiment

Make sure your mini cups of cool and warm water go into the freezer at the same time.

Once all the mini cups are in the freezer, it's time to start.


• Wait for around 80 minutes and then fetch some mini cups from the freezer

• Test a C cup and W cup and mark down how frozen the water is on your worksheet

• If either of them is completely frozen mark down the time on your sheet

• Wait 10 minutes and repeat.

Keep checking!

Keep checking new mini cups from the freezer until water in both the C and W cups is frozen solid. Make sure you write down on your sheet the time at which they froze and which was first. Once they have both frozen, it's time to think about your results.

Make sure your mini cups of cool and warm water go into the freezer at the same time.

Discuss the results

Does warm water freeze faster than cool water?

  • Has the investigation given you an answer?
  • Did you find a difference in freezing times?
  • Did all the groups get the same result?
  • If there was a difference what could have caused it?
  • Are the results valid? Did we control variables well?
  • Was our measurement accurate? How could it be improved?

Write a summary

“I used to think that... But now I know that... Because...”

Water - Teaching resources
Water - Investigations additional resources
Water - Special Educational Needs and Disability resources