Water is a natural resource that is vital for human survival and health, although only a tiny fraction of the Earth's supply is available to humans and terrestrial animals. In this unit we look at threats, such as pollution, to water's capacity to support life around the world. This study unit is just one of many that can be found on LearningSpace, part of OpenLearn, a collection of open educational resources from The Open University. Published in ePub 2.0.1 format, some feature such as audio, video and linked PDF are not supported by all ePub readers.