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How does water hardness vary?

Water hardness levels vary across the country and depend on the type of land you live onLevels also vary from season to season as a result of the amount of rainfall. Water hardness is a measure of the amount of calcium and magnesium in the water solution. So the types of rocks and the geological makeup of the ground beneath you will impact your local water hardness.  

For example, softer rocks like limestone and chalk commonly found across the UK contain lots of calcium and magnesium.  

Rainwater is naturally softAs rainwater falls to the ground and passes through rocksthe minerals (calcium or magnesium carbonate) in the rocks are dissolved in the water, making it harder. 

This water is then stored in the ground until it enters our water supply systems and then our homes. The length of time the water is stored in the ground and the speed it flows through our rocks and soil can also affect the amount of calcium and magnesiumaffecting the water hardness level and quality.  

In a period of heavy rain, the water moves through the ground quickly, picking up fewer mineral deposits and diluting the hardness. When there is less rainfall, the hardness becomes more concentrated as the water stays in the ground for longer and absorbs more minerals.  

In the UK, there are different ways of measuring water hardness. Parts per million (ppm) is the modern metric system for units of hardness of water. Before that, the degree Clark method was used to measure hard water levels.  

Across the UK, many people suffer from the effects of hard water. If you’re unsure whether you have hard water in your home, try our water quality test to find out how hard the water is in your area. Learn about your water hardness here.