Water Pollution and Its Control: Causes and Solutions

Water pollution is contamination of rivers, lakes, groundwater and oceans by sewage, industrial waste, fertilisers and chemicals, making water unsafe for drinking, farming and aquatic life.

Clean water is limited although Earth looks blue. Polluted water spreads diseases like cholera and diarrhoea, kills fish and increases treatment costs. Preventing pollution is cheaper than cleaning it later.

Key Concepts

Point source is pollution from a single identifiable outlet like a factory pipe. Non-point source is diffuse, like fertiliser runoff from fields. Biochemical Oxygen Demand (BOD) is oxygen needed by microbes to decompose organic waste, measured in milligrams per litre (mg L-1); higher BOD means more pollution. Eutrophication is nutrient enrichment causing algal blooms and oxygen depletion. Dissolved Oxygen (DO) below about 4 mg L-1 stresses many fish.

How It Works

1. Untreated sewage adds organic matter and pathogens to water.
2. Microbes decompose organics and consume dissolved oxygen, raising BOD.
3. Excess nitrates and phosphates from farms cause algae to grow fast; when algae die, decomposition uses more oxygen.
4. Toxic metals and pesticides accumulate in organisms through biomagnification.
5. Treatment plants remove solids, organics and nutrients in primary, secondary and tertiary stages before release.

Worked Example

A river sample has BOD of 30 mg L-1 upstream of a town and 120 mg L-1 downstream after sewage inflow.

Step 1: Increase = 120 - 30 = 90 mg L-1.

Step 2: Ratio = 120 / 30 = 4. Downstream BOD is four times higher.

Step 3: Clean water for aquatic life usually needs BOD below about 3 mg L-1, so both values indicate pollution and downstream is severe.

The jump shows the town is adding a large organic load needing treatment.

Common Misconceptions

• Water cleans itself completely. Rivers have limited self-purification; overload overwhelms it and groundwater stays polluted for years.
• Clear water is safe to drink. Bacteria, viruses and dissolved chemicals are invisible.
• Only factories pollute water. Households, farms and storm runoff are major sources too.

Real-World Applications

Sewage treatment plants in cities use activated sludge to cut BOD before discharge. Farmers use soil testing and drip irrigation to reduce fertiliser runoff. Industries must install effluent treatment plants and reuse water. Constructed wetlands naturally filter wastewater in many eco-projects. Regular testing of drinking water sources for bacteria and chemicals, protection of catchment areas, ban on dumping solid waste into drains, and community awareness about not using water bodies for washing or idol immersion without safeguards help keep pollution loads low.

In summary, water pollution comes from point and non-point sources, raises BOD and lowers oxygen through eutrophication, and control needs treatment, regulation and responsible farm and household practices.