CAUSES OF WATER POLLUTION
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.
Fertilizers / Nutrient Pollution
Many causes of pollution, including sewage, manure, and chemical fertilizers, contain "nutrients" such as nitrates and phosphates. Deposition of atmospheric nitrogen (from nitrogen oxides) also causes nutrient-type water pollution.
Mining
Mining causes water pollution in a number of ways:
• The mining process exposes heavy metals and sulfur compounds that were previously locked away in the earth. Rainwater leaches these compounds out of the exposed earth.
• Similarly, the action of rainwater on piles of mining waste (tailings) transfers pollution to freshwater supplies.
• In gold mining, cyanide is poured on piles of mined rock to chemically extract the gold from the ore. Some of the cyanide ultimately finds its way into nearby water.
• Huge pools of mining waste "slurry" are often stored behind containment dams. If a dam leaks or bursts, water pollution is guaranteed.
Chemical and Industrial Processes
Almost all bodies of water in the world have some level of pollution from chemicals and industrial waste. Most hazardous liquid waste solvents, heavy metals, and radioactive materials are injected directly into deep groundwater via thousands of "injection wells."
Personal Care Products, Household Cleaning Products
Whenever we use personal-care products and household cleaning products, we should realize that almost all of it goes down the drain. Studies have shown that up to 90% of your original prescription passes out of you unaltered.
Sewage
In developing countries, an estimated 90% of wastewater is discharged directly into river sand streams without treatment. Even in modern countries, untreated sewage can send disease-bearing water into river sand oceans. Leaking septic tanks and other sources of sewage can cause groundwater and stream contamination.