The water that comes out of your taps at home is very different from the water found in rivers and lakes. The water companies remove both of these during the treatment process. Solid particles are removed by a process called coagulation. This involves the addition of aluminium or iron ions, which attract the small negatively charged particles so that they comes together to form a precipitate. Disinfection of the water is achieved by adding chlorine.
Chlorine is very soluble in water so is simply dissolved in the supply.
Often, ammonia is added to the water after chlorination to form chloramines . These are less effective than free chlorine in killing bacteria, but have the added advantage of persisting longer in the pipes that supply homes and businesses. This is called a residual disinfectant. Another chemical that is sometimes used is sulphur dioxide. This removes excess chlorine, allowing the dosing to be carefully controlled.