How Water is Treated
Raw water from various sources is conveyed by pipelines to the waterworks where it is chemically treated, filtered and disinfected. Treatment frees the water of harmful bacteria and suspended particulate matters including those in the micron range, makes it clear, sparkling, odourless, colourless, and safe for consumption.
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Most treatment plants use chemical coagulation and rapid gravity filtration to remove suspended particulate matters in the raw water. For chemical coagulation, correct doses of suitable coagulants and coagulant-aids are added to the raw water to combine or 'flocculate' the colloidal and larger particles of suspended matter. This causes the suspended matter to settle more readily and then be removed in the sedimentation tank. The water is then passed through rapid gravity filters which remove the finer particles of suspended matter.
At Chestnut Avenue and Choa Chu Kang Waterworks, the suspended particles are removed by membrane filtration. The filtered water, on its way to the clear water tank, where it is temporarily stored, is disinfected with chlorine to get rid of all harmful bacteria and viruses. Finally, the water goes through a series of water quality tests before it is piped to the customers.
Aluminium sulphate is the main coagulant. In most cases, hydrated lime is also added to adjust the pH of the raw water for the best flocculation results. Polyelectrolyte is used as a coagulant aid. For disinfection, chlorine is used to destroy the bacteria and viruses. Ozone is used, as well as chlorine, at Choa Chu Kang and Bedok Waterworks. Ammonia is added in the treated water containing free chlorine to form a stable chlorine residual. Activated carbon is also used to remove any bad taste and odour.
Sodium silicofluoride is added to the water on its way from the filters to the clear water tank. Fluoridation is a requirement by the Ministry of Health and has been a practice since 1957. It helps in the prevention of dental caries.