HONG KONG • A lead-contaminated water scandal sweeping public housing estates keeps snowballing, with residents of a luxury private development in Kowloon joining thousands fearing they have unsafe levels of lead in their bloodstreams.

Tests at The Caldecott, where some of its 44 units have sold for around HK$16,500 (S$2,960) per sq ft, have shown lead levels in water almost double the safe limit set by the World Health Organisation.

More than 15,000 households across Hong Kong have been affected since the lead scare surfaced last month, with three more public housing estates this week discovering they had excessive levels of the metal in their tap water.

The government has installed temporary water pipes, provided blood tests and mounted water filters for residents. Earlier, a water sample from a unit at Hung Hom Estate, also in Kowloon, tested at 44.4 micrograms of lead per litre of water - the highest level so far and more than four times the WHO's drinking water guideline of no more than 10mcg.

The finding at The Caldecott of 19 mcg of lead in water from a kitchen serving the banquet hall has prompted the management firm to test all the apartments in the Cheung Sha Wan project.

A spokesman for Guardian Property Management confirmed the result - from a water sample taken on July 17 - but said residents were not panicking, the South China Morning Post (SCMP) reported.

"Some minor irregularity was spotted in a recent water test. The issue is being followed up," the spokesman said.

Political groups have been running their own tests at private and public estates since Democratic Party lawmaker Helena Wong Pik Wan highlighted the problem at Kai Ching Estate last month.

Questions have been raised about what materials were used in installing the water supply network, as well as the welding material used in sealing the connecting pipes.

When asked for possible reasons for the 44.4mcg level of lead in the Hung Hom flat, Water Supplies Department chief chemist Chau Kin Man was quoted by the Standard newspaper as saying: "It may be related to the resident's water consumption habits, such as the volume of water used every day."

Meanwhile, 33 residents of Kwai Luen Estate phase two have been found to have excessive lead in their blood. Twenty-four are children under the age of six, eight are breast-feeding mothers and one is pregnant, the newspaper reported.

Democratic Party vice-chairman Andrew Wan Siu Kin, convenor of the Drinking Water Victims Alliance, called the situation a "social disaster". The increasing number of public housing estates swept up in it exposed "a huge loophole" in the construction, supervision, and use of building material in the city's housing developments, he said.

"This is a social disaster which will only roll bigger and bigger like a snowball," Mr Wan said on RTHK radio. "And it's especially true for housing built in the past 10 years, as there's so much material bought from mainland China," he was quoted as saying by the SCMP.

On Monday, the Water Supplies Department said lead had been used in taps and valves but insisted that was legal.

Secretary for Transport and Housing Anthony Cheung Bing Leung, meanwhile, said the situation is not out of control.