Water Pollution

Prerequisites

• Air Pollution, for the pollution control boards and basic terms.
• Ecosystems, for food chains and nutrient cycles.
• Rivers of Chhattisgarh, for the Mahanadi, Seonath, Kharun, Hasdeo and Kelo.

The Hook: A Village That Could Not Trust Its Wells

Why it matters: Prelims asks about BOD, eutrophication, biomagnification, diseases caused by specific contaminants (Minamata, itai-itai, blue baby) and the Water Act. Mains asks about river pollution, groundwater contamination and remedies, where Chhattisgarh’s rivers and arsenic belt are natural examples.

Sources of Water Pollution (जल प्रदूषण)

Measuring Water Quality

CPCB designated best-use criteria (selected):

The CPCB treats a river stretch as polluted when BOD exceeds 3 mg/L, and ranks polluted stretches in Priority I to V (Priority I is the worst, with BOD above 30 mg/L; Priority V is the least severe, with BOD of 3–6 mg/L).

Key Processes

Eutrophication (सुपोषण)

1. Fertiliser runoff and sewage add nitrates and phosphates to a lake or slow river.
2. Algae multiply rapidly (algal bloom). Free-floating plants such as water hyacinth spread.
3. When the algae die, bacteria decompose them and use up the dissolved oxygen.
4. Fish die; the water body slowly fills and ages faster than it naturally would.

Eutrophication is natural over centuries; human-caused cultural eutrophication speeds it up to years.

Biomagnification (जैव आवर्धन)

Some pollutants are persistent (not broken down) and fat-soluble, so they build up in living tissue. Their concentration rises at each step up the food chain.

graph LR
    A["Water
trace DDT"] --> B["Zooplankton
higher"]
    B --> C["Small fish
higher still"]
    C --> D["Large fish
much higher"]
    D --> E["Fish-eating birds
highest: thin eggshells"]

• Classic examples: DDT (thin eggshells in fish-eating birds) and mercury (methylmercury in fish).
• Bioaccumulation is build-up within one organism over its lifetime; biomagnification is the increase across trophic levels.

Contaminants and the Diseases They Cause

Drinking water limits (BIS standard IS 10500:2012), selected:

Small amounts of fluoride protect teeth; only the excess causes fluorosis. For arsenic, quote the 0.01 mg/L acceptable limit (the same as the WHO guideline value); the relaxation allowed for arsenic has been revised over time, so avoid quoting a permissible figure.

Other forms

• Thermal pollution: hot cooling water from power plants lowers DO and harms fish. Cooling towers and cooling ponds reduce it.
• Oil spills: an oil film blocks oxygen exchange and coats seabirds. Bioremediation uses oil-eating bacteria (see Soil and Noise Pollution for Oilzapper).
• Microplastics: plastic fragments smaller than 5 mm, now found in rivers, seas, fish and drinking water.

Treating Wastewater

The sludge from secondary treatment goes to anaerobic digesters, where bacteria produce biogas (mainly methane). This is standard NCERT Class XII biology and a favourite Prelims question.

Laws, Institutions and Programmes

Analysis for Mains

Why rivers stay polluted

1. Sewage treatment gap: cities generate far more sewage than their treatment plants can handle, and many plants run below capacity.
2. Industrial effluent standards are poorly monitored; small units often bypass treatment.
3. Non-point sources (fertiliser runoff) are hard to regulate.
4. Reduced river flow from dams and abstraction lowers the river’s ability to dilute and self-purify.
5. Groundwater contamination by geogenic arsenic and fluoride is invisible and slow to show symptoms.

Way forward

• Decentralised sewage treatment and faecal sludge management in small towns.
• Zero liquid discharge for highly polluting industries and real-time effluent monitoring.
• Balanced fertiliser use (Soil Health Cards) to cut nitrate runoff.
• Ensuring environmental flow in rivers.
• Regular testing of village sources under Jal Jeevan Mission, and safe surface-water supply in arsenic and fluoride areas.

Memory Tricks

Don’t Confuse

Common Mistakes

Practice

All questions below are original practice questions written in CGPSC style. They are not previous-year questions.

Level 1: Foundation

1. Excess nitrate in drinking water causes ______ in infants.
2. The BOD test conventionally measures oxygen uptake over ______ days.
3. In which block of Chhattisgarh is groundwater arsenic contamination well documented?

Level 2: Prelims MCQs

Q1. Consider the following statements:

1. A high value of biochemical oxygen demand (BOD) indicates a high level of organic pollution.
2. Chemical oxygen demand (COD) of a water sample is generally lower than its BOD.
3. Eutrophication eventually lowers the dissolved oxygen of a water body.

Which of the statements given above is/are correct?

• (a) 1 only
• (b) 1 and 3 only
• (c) 2 and 3 only
• (d) 1, 2 and 3

Q2. Match List I (Contaminant) with List II (Health effect):

• (a) A-3, B-1, C-2, D-4
• (b) A-1, B-3, C-2, D-4
• (c) A-3, B-1, C-4, D-2
• (d) A-3, B-2, C-1, D-4

Q3. The phenomenon in which the concentration of DDT increases at successive trophic levels of a food chain is called:

• (a) Bioaccumulation
• (b) Biomagnification
• (c) Bioremediation
• (d) Eutrophication

Q4. Which of the following rivers of Chhattisgarh have had stretches identified as polluted in CPCB assessments?

1. Kelo
2. Kharun
3. Hasdeo
4. Indravati

Select the correct answer:

• (a) 1 and 2 only
• (b) 2 and 4 only
• (c) 1, 2 and 3 only
• (d) 1, 2, 3 and 4

Q5. In a sewage treatment plant, the major reduction in BOD takes place during:

• (a) screening
• (b) primary sedimentation
• (c) secondary (biological) treatment
• (d) chlorination

Level 3: Mains Answer Writing

Q1. (60 words) What is eutrophication? State two ways to prevent it.

Q2. (150–200 words) Examine the causes of river and groundwater pollution in Chhattisgarh and suggest remedial measures.

Quick Revision Table

Key Takeaways

What’s Next

• Soil and Noise Pollution, the next topic in this chapter
• Air Pollution, the previous topic
• Environmental Conventions, for the Minamata and Stockholm conventions
• Life Science and Human Health, for water-borne diseases
• Mineral Resources and Mining Belts, for mining’s impact on rivers