The sources of water pollution can be put into two categories.
1. Point Sources:
These are sources of water pollution that occur when toxic substances enter directly into the water. These include:
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i. Sewage:
Untreated domestic wastes like human excreta and detergents are discharged into water bodies. When these wastes get into the water, they breed pathogens. Since they are not treated properly, they contaminate the water that we later consume. These are also called municipal point sources and include treatment plants, utility stations, motor pools and fleet maintenance facilities.
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ii. Industrial discharges:
Industrial wastes contain harmful chemicals, non-biodegradable wastes, radioactive wastes, thermal matter and suspended solids. Industrial effluents are so harmful that they may poison wastewater treatment plants as well. Since it is difficult to break down industrial wastes, they cause enormous harm to the water.
2. Non-point sources:
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Non-point sources of pollution change water qualities indirectly through environmental changes. These include:
i. Agricultural run-offs:
Pollutants from agricultural lands that are washed off and enter the water are a major source of water pollution. Forests are depleting and more and more run-off from agricultural lands is flowing into the water bodies. The chemical fertilizers and pesticides used on the crops these days are harmful for the environment because of high levels of nitrates and phosphates. These chemicals contaminate the waters due to irrigation, rainfall and drains.
They contaminate the water and aquatic life is at risk. Some of the harmful elements of agricultural effluents can also enter the food chain and cause harm to all living organisms. They also create an imbalance in the nitrogen and phosphorus levels in water, which makes the water unhealthy for watering plants.
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ii. Thermal pollutants:
Thermal pollutants are a result of nuclear activity, atomic power plants and thermal plants. These plants release wastes that are heated up. They warm the water in turn, making it inappropriate for use. Increase in temperature of water results in growth of algae. High temperature of water also reduces the flow of oxygen, making it difficult for the living organisms to breathe. Radioactive compounds in water cause fatal diseases like cancer and even results in damage to genes.
iii. Detergents:
Inorganic pollutants like acids, salts, detergents and toxic metals pollute water. These newly-found wastes comprise compounds that make the water unfit for use. Detergents, for instance, primarily comprise of phosphate. The synthetic detergents that are present in domestic sewage increase the phosphate levels in water, making it difficult to use.
iv. Siltation:
When soil and soil particles flow into the water, they result in a layer in the sea that not only allows more algae to grow, but also reduces visibility in the water. While the algae are harmful for the water, the lack of visibility results in low penetration of light into the water. This harms the photosynthetic activity in the water, risking the lives of the plants there.