cryptosporidium

Waterborne parasite that causes disease in humans and other animals. It has been found in drinking water in the UK and USA, causing diarrhoea, abdominal cramps, vomiting, and fever, and can be fatal in people with damaged immune systems, such as AIDS sufferers or those with leukaemia. Just 30 cryptosporidia are enough to cause prolonged diarrhoea.

Conventional filtration and chlorine disinfection are ineffective at removing the parasite. Slow sand filtration is the best method of removal, but the existing systems were dismantled in the 1970s because of their slowness.