A common disinfectant used for water treatment is a 15% solution of Sodium Hypochlorite NaClO (Chlorination). It is made by reacting Sodium Hydroxide with Chlorine
2NaOH + Cl2 = NaCl + NaClO + H2O
Chlorination of drinking water can oxidize organic contaminants, producing trihalomethanes (also called haloforms), which are carcinogenic.
One way to solve this problem is to use membrane filtration to filter off the precursors of halogenated products.