Large bodies of water are all around us: rivers flow through our towns and cities, inland lakes collect pools of fresh water, and the salty ocean covers nearly two-thirds of the Earth's surface. In this volume, readers will learn about the importance of these three natural sources of water, as well as their similarities and differences. Emphasis is also placed on the relationship between humans and these various water sources, both in terms of constructive use of these precious resources and the risks inherent in pollution. Readers will walk away with a better comprehension of the science behind bodies of water and the delicate balance of the ecosystem.