Water treatment is the way we clean water to make it safe for people to drink. Even when water looks clear, it can carry tiny things like germs and chemicals we can’t see.

Water is a good solvent, which means it can mix with a lot of things easily. That includes natural pollutants, like dust, minerals and pollution. In nature, water is not always clean enough for people to drink.

When the microscope was invented in the 1850s, germs could be seen in water for the first time. In 1902, Belgium was the first country to use chlorine to clean water in a public water supply. (Chlorine helps kill germs and make water safe. It’s why many pools use chlorine, too.)

Today, almost every city in the world treats their drinking water.

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