Excess chromium in water purification lime: water board suspends 37-tonne stock

The National Water Supply and Drainage Board (NWSDB) has suspended the use of a 37-tonne stock of hydrated lime (calcium hydroxide), a chemical used in water purification. Internal laboratory testing found its chromium level exceeded the recommended limit by 58 percent.

Tests by the NWSDB's central laboratory found chromium at 19 mg/kg in the consignment, against a recommended level of 12 mg/kg. The chemical is used in water supplied to the public.

A group including NWSDB experts and professors from two universities is studying the next steps, including whether compensation can be claimed from the supplier, NWSDB chairman A.M.P.C.T. Bandara said. Although a second test by the Sri Lanka Standards Institution laboratory found chromium at 11 mg/kg, the consignment has not been used. "We are now carrying out chemical purification using another batch," Bandara said.

Retired NWSDB water purification expert Nihal Ratnayake said hydrated lime is generally used at five milligrams per litre of water. "If there is no alternative, this stock could be used for a short period, but continued use is not advised," he said.

In line with European best practices, Sri Lanka maintains high standards. The NWSDB has a network of 36 water and wastewater testing laboratories, and drinking water is assessed against the Sri Lanka Standard SLS 614, which the government says aligns with WHO recommendations.