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WATER POLLUTION — POINT AND NONPOINT SOURCES
There are many specific causes of water pollution, but before we list the toppers, it's important to understand two broad categories of water pollution:
“Point source” — occurs when harmful substances are emitted directly into a body of water.
“Nonpoint source” — delivers pollutants indirectly through transport or environmental change.
An example of a point source of water pollution is a pipe from an industrial facility discharging effluent directly into a river. An example of a nonpoint-source of water pollution is when fertilizer from a farm field is carried into a stream by rain (i.e. run-off).
Point-source pollution is usually monitored and regulated, at least in Western countries, though political factors may complicate how successful efforts are at true pollution control. Nonpoint sources are much more difficult to monitor and control, and today they account for the majority of contaminants in streams and lakes.
Now, on to the more specific categories of water pollution causes.
WATER POLLUTION CAUSES — #1
Pesticides
Pesticides that get applied to farm fields and roadsides—and homeowners' lawns—run off into local streams and rivers or drain down into groundwater, contaminating the fresh water that fish swim in and the water we humans drink. It's tempting to think this is mostly a farming problem, but on a square-foot basis, homeowners apply even more chemicals to their lawns than farmers do to their fields! Still, farming is a big contributor to this problem. In the midwestern United States, a region that is highly dependent on groundwater, water utilities spend $400 million each year to treat water for just one chemical—the pesticide Atrazine.
WATER POLLUTION CAUSES — #2
Fertilizers / Nutrient Pollution
Many causes of pollution, including sewage, manure, and chemical fertilizers, contain "nutrients" such as nitrates and...