Aside from the very important issue of clean drinking water, why care about clean water? Clean water – and enough of it – is essential to any and all life, animals, plants, and microbes. Fish are vulnerable to polluted water. Indeed, there are places in the world where the water is so polluted that fish have disappeared. In many other places fish or shellfish survive, but are not safe to eat because their flesh is contaminated. Humans enjoy being around water, but contamination with infectious organisms makes swimming unsafe; or if water has obnoxious odors or scum, being near it is not pleasant. Clean water is vital.

This chapter surveys water pollutants, the problems they cause, and actions taken to reduce them. Section I introduces terms important to understanding water pollution. After then describing the six conventional water pollutants, it introduces toxic and non-conventional pollutants. Section II examines reducing point-source pollution, especially through wastewater treatment. Sewage treatment is a major part of this effort. Section III looks at the control and pollution-prevention methods commonly used to reduce sources of non-point-source pollution. Section IV examines how the impact of pollution differs depending on the type of water body affected (rivers, estuaries, groundwater, and wetlands). Section V delves into water pollution in a developing country, China.