WATER POLLUTION
Water pollution is any change in water quality that can harm living organisms or make the water unfit for human uses such as irrigation and recreation. It usually involves contamination by one or more chemicals or excessive heat (thermal pollution). Sources: Water pollution can come from a single (point)source, or from a larger, more dispersed (nonpoint) source. Point sources discharge pollutants into bodies of surface water at specific locations through drain pipes, ditches, or sewer lines. Examples include factories, sewage treatment plants (which remove some, but not all, pollutants), underground mines, and oil tankers. Because point sources are located at specific places, they are fairly easy to identify, monitor, and regulate. Most of the world’s more-developed countries have laws that help control point-source discharges of harmful chemicals into aquatic systems. In most of the less-developed countries, there is little control of such discharges. Nonpoint sources are broad a