PUB, the national water agency, thanks Ms Joan Chng for her letter ("Is powder used to clean HDB walkways safe?"; Forum Online, Aug 9).
The drains in HDB estates are connected to the public drainage system. Drains are meant to collect rainwater, which is eventually conveyed to the reservoirs or to the sea.
Washing of common areas in HDB estates is usually carried out using high-pressure water jets.
The white powder that Ms Chng pointed out is likely to be bleaching powder, which contains calcium hypochlorite. Bleaching powder, if sparingly used for specific cleaning purposes, does not have an impact on the quality of water in our reservoirs.
The public can provide feedback by calling PUB's 24-hour call centre at 1800-284-6600.
Catchment and Waterways