The document discusses the hydrosphere and water pollution. It defines the hydrosphere as the combined mass of water found on, under, and over the surface of a planet. It notes that Earth's hydrosphere contains 1.4 x 1018 tonnes of water, with 75% of the surface covered by oceans. It also discusses Europa's subsurface ocean. The document then covers the hydrological cycle and causes of water pollution, noting pollution is a major global problem responsible for millions of deaths annually from diseases like diarrhea. Organic and inorganic pollutants are listed. Effects of pollution include damage to bodies of water like Boston Harbor from toxic waste and sewage.