Hong Kong enjoys one of the safest water supplies in the world. The quality of supply conforms to the Guidelines for Drinking-water Quality recommended by the World Health Organization (1993) and is checked by extensive sampling at water treatment works, distribution network and customers taps.
The water supply is derived from surface water resources and is fully treated by predisinfection by chlorine, coagulation using aluminium sulphate and hydrated lime, rapid gravity filtration preceded by sedimentation at most water treatment works, pH value correction with hydrated lime, final disinfection by chlorination, and fluoridation for dental protection. Chlorine is widely used worldwide as disinfectant for drinking water. A trace amount of residual chlorine is maintained in the supply system in order to safeguard the water from possible contamination. Pathogenic bacteria and macroscopic organisms as well as heavy metals and pesticides are removed in the water treatment process.
Clause 24 of the Waterworks Regulations (Subsidiary) stipulates that water purifiers / filters shall not be installed or used without the permission in writing of the Water Authority and off-tank supply may be required to avoid the possibility of contamination of the mains water supply system.
As the water supply in Hong Kong conforms to the Guidelines for Drinking-water Quality recommended by WHO, WSD does not recommend the installation of water filters because they may become ideal breeding grounds for bacterial growths and give rise to health hazards if they are not properly maintained.
However, WSD would not take action to demand consumers to remove the installations if such are found on the inside service at the consumers premises where the water quality may have been affected by lack of proper maintenance of the water storage tanks or by corrosion of the water pipes on the inside service. For these cases, warnings are normally given to the consumers to discourage them from the use of filters and to remind them on the need of proper maintenance of their water tanks and water pipes.