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In this investigation, pupils tested the hardness of their school tap water and looked at which froze first between samples of warm and cool water.

We are displaying the results submitted by schools across the UK on a map of the country. The map key shows five discs of different colours, which represent the five levels of the water hardness scale - from water hardness 1 (soft water) to water hardness 5 (hard water).

The key also displays two symbols: a snowflake on blue background, and three curved vertical lines on red background. The former is displayed when the samples of cool water froze faster; the latter when warm water froze first. Each cluster on the map is represented by a symbol that joins the two results. For example, an area where the water was a 5 on the hardness scale and cool samples froze first will be represented by a purple circle with a snowflake in the middle.