Water Pollution
NCERT Class 12 • Biology • Chapter "Environmental Issues" | NCERT Class 8 • Science • Chapter "Pollution of Air and Water"
Water Pollution
Water pollution is the addition of any substance to water that makes it unfit for its intended use. Because water dissolves so many substances and moves through the whole landscape, contamination at one point spreads far beyond it and reaches drinking supplies and crops alike.
Sources and Indicators
- Domestic sewage is the largest source in India and carries organic waste, detergents and disease causing organisms.
- Industrial effluent carries heavy metals such as mercury, lead and cadmium, along with acids, alkalis and dyes.
- Agricultural runoff carries fertiliser, pesticide and animal waste into rivers, lakes and groundwater.
- Biological oxygen demand is the amount of oxygen needed by microbes to decompose the organic matter in a water sample.
- A high biological oxygen demand means heavy organic pollution, because more oxygen is being consumed.
- Eutrophication is the excessive growth of algae caused by fertiliser runoff; when the algae die and decompose, oxygen falls and fish suffocate.
- Thermal pollution is the release of hot water from power plants, which lowers the dissolved oxygen the water can hold.
Effects and Control
- Contaminated water spreads cholera, typhoid, hepatitis, dysentery and other waterborne diseases.
- Heavy metals accumulate in the body and cause long term nerve, kidney and bone damage.
- Pesticides undergo biomagnification and reach their highest concentration in top consumers.
- Groundwater contamination by fluoride, arsenic and nitrate is a serious problem in several regions.
- Control begins with treating sewage and effluent before discharge rather than after.
- Treatment has primary physical, secondary biological and tertiary chemical stages.
- Reducing fertiliser and pesticide use, watershed management, rainwater harvesting and river cleaning programmes complete the response.
- Wetlands and constructed reed beds can treat waste water naturally at low cost, which suits small towns well.
- Safe drinking water depends on protecting the source, not only on treating the water afterwards.
| Source | Main Pollutant | Main Effect |
|---|---|---|
| Domestic sewage | Organic waste, pathogens | Waterborne disease |
| Industrial effluent | Heavy metals, acids | Long term poisoning |
| Agricultural runoff | Fertiliser and pesticide | Eutrophication, biomagnification |
| Power plant | Hot water | Lower dissolved oxygen |
Eutrophication — the excessive growth of algae in a water body caused by nutrient enrichment, which lowers the oxygen available to other life.
Exam me kaise aata hai
- Excessive algal growth from fertiliser runoff is — eutrophication
- Oxygen needed to decompose organic matter is measured as — biological oxygen demand
- Release of hot water into a river is — thermal pollution
- High biological oxygen demand indicates — heavy organic pollution
UPSC/State PSC ke liye
- Eutrophication kills fish not by poisoning them but by removing oxygen, which is why a nutrient can be as deadly as a toxin.
- A high biological oxygen demand is an indirect measure: it shows how much oxygen microbes will consume, and therefore how little will be left for aquatic life.
Yahan confuse hote hain
✗ Fertiliser in water is harmless since it is a nutrient | It causes eutrophication and oxygen loss | ✓
✗ High biological oxygen demand means clean water | High demand means heavy organic pollution | ✓
✗ Thermal pollution adds chemicals to water | It adds heat, which lowers dissolved oxygen | ✓
Ek nazar me
- Sewage, industrial effluent and agricultural runoff are the main sources.
- High biological oxygen demand indicates heavy organic pollution.
- Eutrophication and thermal pollution both act by lowering dissolved oxygen.
- Control means treating waste before discharge and reducing chemical use.