The drying Paraibuna dam, part of the Cantareira water system that provides greater São Paulo in Brazil with most of its water. Photograph: Roosevelt Cassio/Reuters
Water is the driving force of all nature, Leonardo da Vinci claimed. Unfortunately for our planet, supplies are now running dry – at an alarming rate. The world’s population continues to soar but that rise in numbers has not been matched by an accompanying increase in supplies of fresh water.