Perfluoroalkyl substances - or PFAS - are a group of thousands of man-made chemicals which have been widely used in everything from frying pans to firefighting foam. Anything which is non-stick, water-resistant or stain-repellent is likely to have been produced using PFAS. In the USA they have been linked to mass poisoning of water supplies, as the Hollywood film 'Dark Waters' documented. In this programme, Leana Hosea sets out to discover whether they are having an impact here. She teams up with environmental journalist Rachel Salvidge to investigate. They take water samples from drinking water around the country and have them analysed for the presence of PFAS. In Jersey Leana meets residents who believe their ill health is down to contamination of their drinking water, and whose blood has been shown to contain PFAS. She hears what the links are with health concerns, and finds out why firefighters are an at-risk group. Producer: Emma Campbell