But it rejected calls to carry out tests at all public housing estates built after 2005, claiming that random sampling would be representative enough. About a third of the samples are expected to come from public housing estates, reflecting the current ratio of public to private flats.

The new two-tier sampling system will include a “random day time test” of one-litre samples straight from the taps, subject to further verification tests if metals are found to exceed acceptable levels.

This requires letting taps run for five minutes and then leaving the water to stagnate in pipes for 30 minutes before further one-litre samples are drawn.

The recommendations adopted were made by a government panel of international experts on drinking water safety.

The past practice of running the water first before collecting a sample was severely criticised at the height of the lead contamination scandal.

“What we’re doing is actually on par with many advanced economies in the world. For a city of seven million people, we are going for a sample size that is higher than a lot of other comparable cities,” development minister Michael Wong Wai-lun said.

He denied that the previous testing method was deficient, saying instead that Hong Kong should “move with the times”.

Director of Water Supplies Enoch Lam Tin-sing said data would be collected and used as a basis to adopt standards on par with or even beyond WHO guidelines in the future.

“We will take about three to five years to collect the data we need and then consider reviewing or raising these standards if necessary,” he said.

The new action plan also proposes the establishment of an independent “Water Quality Regulator” – under the Development Bureau – which will be advised by a committee of academics and medical experts overseeing the safety of drinking water.

Subsequent government tests found excess lead in dozens of water samples drawn from 11 public housing estates across Hong Kong.

Lapses in tainted water scare: Carrie Lam concerned about similar ‘phenomena’ in other departments

The effects of the tainted water scare are still being felt. Of the 5,655 voluntary blood tests provided by the government for residents in the wake of the scandal, 165 people were found to have mildly elevated levels of lead in their blood.

As of last month, at least five people from the tests were found to still have mildly elevated levels of lead in their blood.

Of the 126 children with elevated blood lead levels assessed for development delays, nine were still showing signs as of last month and were being rehabilitated. But the government said it was hard to prove if it was a result of lead exposure.

The department said on Thursday it would continue to update its plumbing material standards and move ahead with legislative amendments to define the duties of licensed plumbers and plumbing contractors.

Building owners and property management companies will also be encouraged to come up with their own water safety plans through a new voluntary management scheme on the quality of drinking water.

Just a fifth of the 29,000 households at the 11 public estates affected have had their pipes and taps changed since the scandal broke out.

On Thursday, Director of Housing Stanley Ying Yiu-hong said it would be difficult to lay out a timetable for the replacement of all pipes and fittings because consent from residents was required.

The construction would then have to be done on a case-by-case basis to minimise the impact on homes.

Meanwhile, the Housing Authority said it supported the implementation of the action plan.

Democratic Party lawmaker Helena Wong Pik-wan said the sampling method failed to tackle the root of the problem, which was the use of leaded solder in the plumbing system.

Pro-establishment lawmaker Edward Lau Kwok-fan said the government should honour its promise and test for lead at all public housing estates to give residents “peace of mind”.