Sugar Cube in the Pool: London Passes Clean Water Test

An Imperial College citizen study of 8,000 samples finds London tap water safe from PFAS, well below strict UK and European safety thresholds

22 May 2026

For years, the British public has been told to worry about what flows from its taps. Fears over "forever chemicals", or PFAS, frequently make the news. Yet when residents in 28 London boroughs filled their kettles recently, they were unwittingly participating in a massive reality check.

A study by Imperial College London tested nearly 8,000 water samples from households and public fountains. The results should soothe anxious gulps. Not a single sample breached the safety limits set by British or European regulators. Individual concentrations of the chemicals ranged from a tiny 0.6 to 6.0 nanograms per litre. To make sense of these minuscule numbers, Dr Alexandra Richardson, the lead researcher, noted that 4 nanograms per litre is "equivalent to dissolving one sugar cube in 400 Olympic-sized swimming pools of water."

Londoners can breathe a sigh of relief, but the data reveals a deeper paradox. While water companies have successfully filtered out the worst of these toxins, the chemicals remain stubbornly present in daily life. In fact, tap water accounted for only about a fifth of the participants' total weekly intake. The real culprits are food packaging and consumer goods. Banning a chemical in the factory does not instantly scrub it from the environment. Legacy compounds like PFOA and PFOS, which are already outlawed, were still detectable in the water supply.

This suggests that tightening water regulations yields diminishing returns. It is much easier to test a municipal pipe than it is to police the wrappers on supermarket shelves. Moreover, what holds true for the capital may not apply elsewhere. Previous reports have flagged higher chemical levels in the east and south-east of England. Professor Leon Barron, a principal investigator, argues that the experiment needs to go further: "Conducting a national study of household tap water would enable better understanding of regional variability in the levels of PFAS and other trace chemical pollutants."

New European rules require water suppliers to monitor these substances against strict new thresholds. For now, London’s water managers have a clean bill of health and a solid baseline. The data shows the line is holding. But as compliance becomes mandatory, utility companies may find that keeping drinking water clean is the easy part. The harder battle lies with the products that humans touch long before they turn on the tap.