Water pollution occurs when harmful substances—often chemicals or microorganisms—contaminate a stream, river, lake, ocean, aquifer, or other body of water, degrading water quality and rendering it toxic to humans or the environment.
7. Three Big Ideas
1. There are a number of ways to purify drinking
water, but the most effective and cheapest strategy
is pollution control.
2. The key to protecting the oceans is to reduce the
flow of pollution from land and air, and from
streams emptying into ocean waters.
3. Reducing water pollution requires that we prevent
it, work with nature in treating sewage, cut
resource use and waste, reduce poverty, and slow
population growth.
Editor's Notes
Table 20-1
Table 20-2
Figure 20.A: Scientists measure dissolved oxygen (DO) content in parts per million (ppm) at 20°C (68°F) as an indicator of water quality. Only a few fish species can survive in water with less than 4 ppm of dissolved oxygen at this temperature. Some warm-water species have evolved ways to tolerate low DO levels better than most cold-water species can. Question: Would you expect the dissolved oxygen content of polluted water to increase or decrease if the water is heated? Explain.
Figure 20.7: Natural capital.
A stream can dilute and decay degradable, oxygen-demanding wastes, and it can also dilute heated water. This figure shows the oxygen sag curve (blue) and the curve of oxygen demand (red). Depending on flow rates and the amount of biodegradable pollutants, streams recover from oxygen-demanding wastes and from the injection of heated water if they are given enough time and are not overloaded (Concept 20-2a). See an animation based on this figure at CengageNOW™. Question: What would be the effect of putting another discharge pipe emitting biodegradable waste to the right of the one in this picture?
Figure 20.13: Natural capital degradation.
These are the principal sources of groundwater contamination in the United States (Concept 20-3a). Another source in coastal areas is saltwater intrusion from excessive groundwater withdrawal. (Figure is not drawn to scale.) Question: What are three sources shown in this picture that might be affecting groundwater in your area?
Figure 20.20: Solutions.
Primary and secondary sewage treatment systems help to reduce water pollution. Question: What do you think should be done with the sludge produced by sewage treatment plants?
