Environmental Issues - Water Pollution

Water pollution means any change in the water quality which makes it unsuitable for use by humans and by other living organisms.

Water pollution happens when harmful substances get mixed with water, making it impure or dirty. This means the water is not safe for drinking or using.

• Sometimes, dirt or debris can be seen floating in water, making it look muddy or unclean.
• Some harmful substances dissolve in water and are invisible but still dangerous.
• Water can be unsafe even if it appears clean due to these dissolved substances.
• Polluted water is harmful to humans, animals, and plants, causing illness.
• Rivers and lakes are key water sources that must be kept clean to ensure safe usage.

A polluted water body

• The Water (Prevention and Control of Pollution) Act, 1974, was passed to safeguard water resources. Main sources — domestic sewage, industrial effluents and agricultural run-off.
• BOD (Biochemical Oxygen Demand) is the dissolved oxygen required by microorganisms to decompose organic matter in water. High BOD = high pollution = low oxygen = death of aquatic organisms.
• Algal bloom — excessive growth of planktonic algae due to excess nitrogen and phosphorus. Releases toxins and causes fish mortality. Water hyacinth (Eichhornia crassipes) — "Terror of Bengal" — is an invasive plant that chokes water bodies.
• Eutrophication — natural ageing of a lake by nutrient enrichment. When accelerated by human activities, it is called Cultural/Accelerated Eutrophication, depleting oxygen and killing aquatic life.
• Biomagnification — increase in concentration of toxic pollutants (DDT, mercury) at successive trophic levels. Non-degradable, accumulate in tissues and pass to the next trophic level.
• Thermal pollution — caused by thermal and nuclear power plants releasing hot coolant water, raising water temperature and killing aquatic flora and fauna.