Many water purification methods introduced into the developing world are quickly abandoned as people don’t know how to use and maintain them, says Norma Alcantar at the University of South Florida in Tampa. So she and her colleagues decided to investigate the prickly pear cactus, Opuntia ficus-indica, which 19th-century Mexican communities used as a water purifier. The cactus is found across the globe.

The team extracted the cactus’s mucilage – the thick gum the plant uses to store water. They then mixed this with water to which they had added high levels of either sediment or the bacterium Bacillus cereus.

Householders in the developing world could boil a slice of cactus to release the mucilage and add it to water in need of purification, says Alcantar. “The cactus’s prevalence, affordability and cultural acceptance make it an attractive natural material for water purification technologies.”