There are now 21 water treatment works in Hong Kong with a total output capacity of 4.8 million cubic metres per day.

During the water treatment process, raw water (untreated water) is dosed with chemicals for mixing and then passes to the clarifiers where coagulation and flocculation of the impurities in the water will take place. Settled water then flows into filters of sand or anthracite for removal of the more finely divided suspensions.

The filtered water passes into contact tanks where dosed chlorine and lime are added to disinfect and control the alkalinity of the final treated water. Fluoride is also added to minimise the risk of dental decay. A small amount of residual chlorine is maintained in the water to keep it free from bacteria on the rest of its journey. The final water is pumped into a system of watermains, stored in service reservoirs and then supplied to the public.

Dongjiang Water + Rain Water from Local Reservoirs = Untreated Raw Water
Drinking Water =	Water has been treated by the water treatment works of the Water Supplies Department of Hong Kong Special Administrative Region
Raw Water + Treatment = Drinking Water