A large study of London's tap water has revealed that trace amounts of PFAS 'forever chemicals' are present, but their levels are within UK and EU safety limits.
The analysis, led by researchers at Imperial College London in 2024, is the largest study of its kind to look at levels of per- and polyfluoroalkyl substances (PFAS) in drinking water in a UK city.
It finds that while the chemicals were detected in samples from homes and drinking water fountains across the capital, they were always present at levels well below limits set by the UK's water safety body (UK Drinking Water Inspectorate).
People might be concerned to know that these chemicals are present in our drinking water, but it's crucial to understand the amounts we're talking about are tiny Dr Alexandra Richardson School of Public Health
According to the researchers, their findings suggest that PFAS levels in London's tap water likely present a low risk to human health.
However, they caution that continued independent surveillance of water supplies for PFAS and other chemical pollutants is essential to ensure safe limits are not breached.
Dr Alexandra Richardson, from the School of Public Health at Imperial College London and lead author of the study, said: "In the last 12 months alone, we've seen reports of 'forever chemicals' present in surface, ground and municipal drinking water across the UK. This is understandably a cause for concern for the public as we still don't fully understand the long-term impacts of these chemicals on our health.
"Our research should allay fears about PFAS in London's tap water. Importantly, it also provides a realistic baseline to better study the precise effects of PFAS on human health."
Professor Leon Barron, also from the School of Public Health at Imperial College London and one of the principal investigators, said: "This is the largest study of PFAS in tap water across a major UK city, with nearly 8,000 measurements from 89 households in 28 London Boroughs.
"We have some of the best municipal tap water quality in the world. Only about 20% of the tolerable weekly intake of PFAS came from tap water. While our findings are encouraging, conducting a national study of household tap water would nevertheless enable better understanding of regional variability in the levels of PFAS, and other trace chemical pollutants."
The study, published in the journal Environmental Science: Advances, was conducted in collaboration with King's College London and the UK Health Security Agency (UKHSA). The work was funded by the National Institute for Health and Care Research (NIHR), through the NIHR Health Protection Research Units in Chemical Radiation Threats and Hazards, and Environmental Exposures and Health. Recruitment of participants was supported by the Medical Research Council's Centre for Environment & Health and the Royal Society of Chemistry (RSC).
Complex and evolving research
Sometimes called 'forever chemicals', PFAS are a large group of hard-wearing, long-lasting manufactured chemicals. They are widely used in industry, as well in consumer products like non-stick cookware and food packaging, meaning there are numerous routes for them to enter the water supply.
As PFAS break down very slowly, they can accumulate in the environment and the human body over time. There is some evidence that exposure to PFAS may pose a risk to human health.
Previous research has linked high levels of these chemicals with testicular cancer, thyroid disease, increased cholesterol levels and liver damage. But it is a complex, evolving area and many questions remain about the nature and level of health risks.
One common way that people in the UK are likely to be exposed to PFAS is by drinking tap water in their homes. An RSC report in November 2023 found concerning levels of PFAS in water sources such as rivers, lakes, reservoirs and aquifers in England and Wales.
In 2025, reports emerged of unsafe levels of the chemicals in samples from major water suppliers covering the East, Central and Southeast regions of England. Water companies have measures in place to reduce PFAS alongside other contaminants, but it's not clear how much carries through into tap water, since very few studies have looked at this.
Needles in haystacks
In the latest study, the team took a 'citizen science' approach and sent out sample kits to households that had agreed to take part in the study and collect their tap water. The researchers also directly sampled 12 public drinking water fountains.
The team tested the returned samples for 38 different PFAS compounds, including those that have been directly linked to health conditions. Out of these, 11 PFAS compounds were detected.
As new PFAS compounds are still being developed, it is essential to keep monitoring their presence in the environment and in our bodies to study potential long-term health risks Dr Frederic Piel School of Public Health
The concentration of these individual PFAS ranged from 0.6 ng/L (nanograms per litre) through to 6.0 ng/L. Crucially, all were below the 10 ng/L 'Tier 1' threshold set by the UK Government Drinking Water Inspectorate (DWI) and were therefore deemed as 'low risk'.
The total of all the different PFAS in each individual sample ranged from 3 ng/L to 35 ng/L – similarly within the DWI's 100 ng/L low risk threshold for this metric. The values were also well within the EU Drinking Water Directive guidelines/limits.
"Understandably, people might be concerned to know that these chemicals are present in our drinking water, but it's crucial to understand the amounts we're talking about are tiny," explains Dr Richardson. "To put these levels in context, 4 nanograms per litre is equivalent to dissolving one sugar cube in 400 Olympic-sized swimming pools of water – so we are operating at very small scales. As a consequence, we have very stringent checks and quality controls in the lab so that we can confidently stand behind these numbers."
Dr Frédéric Piel from Imperial College London, who was the other principal investigator on the study, said: "Some of the older PFAS compounds, such as PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonic acid) have been around for decades. Despite being phased out of production and subject to stricter regulations, they persist in the environment and in the water supply. As our study shows, they can still be found in trace amounts in tap water. It is therefore very difficult to disentangle the effects of PFAS on health from lifestyle changes that happen over long periods of time. Furthermore, as new PFAS compounds are still being developed, it is essential to keep monitoring their presence in the environment and in our bodies to study potential long-term health risks."
The bigger picture
The researchers note that while their findings provide a useful snapshot of London's water, the 2023 RSC water source study did show spikes in certain parts of the country. It's unclear if higher levels in water sources carry through as higher levels in tap water in these areas.
Dr Richardson added: "Our results support the view that municipal water treatment is effective. Nevertheless, more research and monitoring is needed to better understand how we are exposed to these compounds through water and other sources, if the levels fall within agreed international safety standards and what the potential health implications may be.
"This type of work is only made possible thanks to the collaboration between scientists and the community. We thank all members of the public who took part in this major 'citizen science' project."
Stephanie Metzger, Policy Advisor at the Royal Society of Chemistry, added: "This study provides important reassurance that PFAS levels in London's tap water are currently within existing safety limits, and it demonstrates the value of rigorous, independent measurement at the household level. At the same time, it reinforces why continued monitoring is essential.
"PFAS are extremely persistent, exposure comes from multiple sources, and scientific understanding of their long term health effects is still developing. That means we cannot be complacent. Studies like this are a vital part of building the evidence base needed to protect public health now, while supporting a broader shift towards better management of these chemicals across their whole lifecycle."
In 2025, Imperial and partners launched a new project to tackle major knowledge gaps regarding PFAS contaminating the UK's waterways. Running from 2025-2029, the UNSaFE project, funded by the Natural Environment Research Council (NERC), will develop and use new testing methods to monitor the compounds in water and wildlife, work with a wide range of partners and investigate PFAS persist in the environment and how ecosystems and organisms can be protected.
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'Occurrence of PFAS in municipal drinking water: a participatory case study in London, UK' is published in Environmental Science Advances. DOI: http://doi.org/10.1039/d6va00076b
