Soldering material used on water pipes with a lead content reaching 41 per cent - 585 times the British Standard of 0.07 per cent lead - was the source of contaminated drinking water, a task force investigating the health crisis announced yesterday. It recommended the Water Authority and Housing Authority step up quality control of all piping, including reviewing relevant legislation, conducting more regular inspections, and centralising the procurement of soldering material. It also called for a change in the soldering method of pipes - such as using compression joints or silver brazing - to avoid lead contamination. Since the scandal erupted in mid-July, when lead levels above the WHO standard of 10 micrograms per litre were found in the drinking water of Kai Ching Estate, Kowloon City, government tests have unearthed 11 public housing estates, three primary schools, and two kindergartens with excessive lead in water. At least 139 residents, mostly children under six, from affected estates had lead levels in their blood above the WHO standard of 5 micrograms per decilitre. "Copper alloy fittings also leach lead but do not result in excessive lead in water," said Dr Chan Hon-fai, a task force member and chairman of the Advisory Committee on Water Resources and Quality of Water Supplies. "Leaded solder joints are the source of excessive lead in drinking water in Kai Ching Estate and Kwai Luen Estate Phase 2." These were the first two public housing estates where excessive lead was detected. Wong Chung-leung, chairman of the task force and the deputy director of water supplies, said the findings would be applicable to the other nine estates. "But this is our preliminary finding, we might go and conduct tests in the other estates later," Wong said. Over the past two months, the task force, made up of academics and experts from relevant government departments, dismantled and tested more than 130 components from the water supply chains of two estates. Results showed that copper alloy valves, taps and solder joints of copper pipes from Kai Ching Estate leached lead from soldered joints. The highest lead level reading was 639.8mcg, found in a hot water pipe at a toilet in Hong Ching House of Kai Ching Estate, after water was being left stagnant inside for 24 hours. Helena Wong Pik-wan, the Democratic Party lawmaker who first exposed the lead scandal, said: "The true culprit of the crisis is not [the solder material]. Who approved the use of these materials? Who installed it? Who regulated it? The true culprit is the Hong Kong government - the Water Supplies Department and Housing Department. They didn't do their job well."