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Water from rivers, lakes and the sea has to be treated to make it safe to use and drink. Different methods are used to do this, such as sedimentation, filtration and chlorination. Learn about fluoridation, desalination and distillation.

This topic covers the role of water as a solvent, and calculations involving solubility of compounds in water.

The properties of hard water have advantages and disadvantages. It is possible to measure the hardness of water, and distillation can be used to soften hard water.