The tap water in Ben Archard’s apartment in the Herne Hill neighbourhood of south London flows through toxic lead pipes, increasing the risk of brain damage to his children and prompting him to pay for bottled drinking water.

Tests carried out by the local authority this year revealed that more than half of the 96 flats on the privately owned estate in Lambeth had lead levels in drinking water above the legally permitted 10 micrograms per litre and 60 “receive or are at risk of receiving water above the safe level for lead in drinking water”.

“It is frightening,” said Archard, an electrician, who along with other residents has been pressing the freeholder to get the lead ripped out and replaced with plastic pipes.

More than 50 years after the installation of lead pipes was made illegal in the UK, millions of homes still have antiquated plumbing made of the toxic metal.

Although no new lead pipes have been installed in the UK since 1970, they are still “prevalent” in properties built before that time across all regions, according to water regulator Ofwat, which has allowed companies to raise £186mn from customer bills to tackle the problem in the five years until 2025.

Dealing with the issue is complicated in the UK because water companies are liable for water quality at people’s taps but the maintenance of the pipework that supplies clean water is shared between the companies and property owners.

The exact number of households affected is unclear but the industry estimates that almost a quarter of the 24.8mn domestic properties across England and Wales still have some lead pipes in their supply network.

Infants are the most vulnerable and at risk of life-long reductions in IQ as well as behavioural problems from even low quantities of the toxin coursing through their bloodstreams, according to the World Health Organization.

But lead exposure, which can come from old paints and contaminated soils, also increases the risk of miscarriage, preterm births, depression, chronic kidney disease and heart attacks in adults, the WHO said.

“There is no level of exposure to lead that is known to be without harmful effects,” the WHO added.

The EU drinking water directive, passed last year, halved the allowed level in water from 10mcg to 5mcg per litre in the bloc. But in the UK there are no plans to adopt a tighter standard for lead, according to the Drinking Water Inspectorate, which is part of the Department for Environment, Food and Rural Affairs.

Lead pipes are mostly replaced on an ad hoc basis — for example when they are discovered through a property renovation or when a customer asks for water to be tested and finds that the lead levels breach legal limits.

But a government-commissioned study last year said this approach would not enable water companies to meet a revised lead water level of 5mcg per litre or lower by 2040.

It recommended that they embark on a “significant programme of work” from 2025 to replace lead pipes up to the kitchen tap in higher risk areas.

This would deliver significant economic benefits to the UK, including savings on healthcare costs, educational support and avoided loss of earnings, the study by the Water Research Centre consultancy said.

“Lead plumbing in public buildings and domestic premises remains a measurable risk to public health,” the DWI said. “Action is needed for the protection of future generations.”

Water companies reduce lead exposure from drinking water by adding orthophosphate, which reduces the amount of lead that dissolves into water.

But phosphorous is also a pollutant, causing algal growths that can kill fish through starving them of oxygen at a time when public concern over the health of our rivers and lakes is rising.

Thames Water, the UK’s biggest water company and supplier to Archard’s property, said that in London the hardness of the water helps protect residents.

Although it said there was almost no lead in the drinking water that leaves its treatment works, it said it was “gradually” replacing lead pipes. Tests are carried out at every stage of the treatment process, including regular lead monitoring at randomly selected properties, it added.

In the US, the replacement of lead pipes has become a key political issue. President Joe Biden declared last year they were “a clear and present danger to our children’s health” and committed $15bn to removing the lead pipes that connect homes.

But in Britain the issue has largely gone under the radar, meaning it is “probably much worse”, said Tim Pye, a member of the Lead Exposure and Poisoning Prevention Alliance, a group of academics and concerned parents who campaign on the prevention of lead poisoning in the UK.

The problem is not just historical. Even if the lead pipes have been removed up to the kitchen tap, many households still have lead plumbing elsewhere and lead solder is still sold in shops, permitted for use in closed central heating systems.

Lara Agbaje, an accountant, had a new bathroom and boiler installed shortly after moving into her 1960s-built home in Stevenage, 30 miles north of London, three years ago.

Tests of the water supply soon after found that lead levels were far above the currently recommended 10 micrograms per litre because the plumber had used lead solder to join the copper pipes.

Both Agbaje and her 8-week old baby tested blood positive for lead exposure, forcing her to spend thousands of pounds gutting the bathroom yet again and removing the lead solder. Agbaje now uses a water filter to remove any remaining traces of lead.

“The situation has affected us greatly and doctors cannot confirm that our baby has not been affected permanently,” Agbaje said.

The DWI said “more work is needed to address the legacy issues of lead plumbing in fittings”.

Back in Herne Hill, Archard, who owns the leasehold to his flat, is still fighting for the pipes to be removed. Although the landlord has installed water filters, this is not as effective because they require frequent replacement and it is unclear who will pay, he said.

Lambeth council said it had told the freeholder to remove the pipes and has been working with the UK Health Security Agency to assess the possible impacts on health.

Questions addressed by the Financial Times to the freeholder through the estate’s property agent met with no response but Archard said the landlord was seeking to gain planning permission for an extra storey on the property and the pipes remained in place.

The situation is “frustrating to say the least”, said Archard.