Water chlorination is the process in which chlorine (Cl2) or hypochlorite add to water. Bacteria and other microbes which live in tap water and chlorine is a killer for it. In particular, chlorination is used to prevent the spread of waterborne diseases. These diseases can have a very destroy effect to people. For example, cholera, dysentery, and typhoid.

Chlorine can have used not only for drinking water but also in water of common using or just water which contain the bacterial and algal residue. And in these cases there are a lot of chlorine for killing all bacteria. It is also named shock chorine. Shock chlorination is performed by mixing a large amount of hydrochlorite into the water. The hypochlorite can be in the form of a powder or a liquid such as chlorine bleach. Water that is being shock chlorinated should not be swum in or drunk until the sodium hypochlorite count in the water goes down to three part per million (PPM) or until the calcium hypochlorite count goes down to 0.2 to 0.35 PPM.

There are different ways for clearing water such as ozonation, chloramination, bromination and iodinization, home filtration, UV radiation and ionizing radiation.

The most popular method for clear water is using chlorine. So there is a reason why a lot of filtration of water so popular nowadays.