Potentially toxic “forever chemicals” have been detected in the drinking water sources at 17 of 18 England’s water companies, with 11,853 samples testing positive, something experts say they are “extremely alarmed” by.

Per- and polyfluoroalkyl substances (PFAS) – a group of 10,000 or so human-made chemicals widely used in industrial processes, firefighting foams and consumer products – were found in samples of raw and treated water tested by water companies last year, according to the Drinking Water Inspectorate (DWI), the Guardian and Watershed Investigations has found.