The continuous movement of water between the earth's surface and the atmosphere sewage 2. pollutes water sources by dumping wastes in rivers, streams, and oceans pesticides 3. the leading cause of water contamination in countries without water treatment plants hydrological cycle 4. a source of water pollution caused by the overuse of pesticides and fertilizers lead 5. caused by an overabundance of organic matter in water supplies putrefaction 6. the decomposition of organic matter by microorganisms petroleum 7. a chemical pollutant that can enter the water cycle through agricultural or domestic use eutrophication 8. can cause the contamination of underground water supplies if poured on the ground industry 9. a metal that leaks into water supplies via the soil or aging water systems agriculture