Topic 21: Water Pollution

Water pollution is the highest-frequency pollution theme in UPSC Prelims and a recurring GS-III Mains anchor. Master four things and you cover most of it: the BOD–COD–DO parameter set, the eutrophication mechanism, arsenic/fluoride geogenic contamination, and the policy chain from the Water Act 1974 to Namami Gange. This file builds each from definition to current data.

UPSC Prelims · Mains GS-III BOD · COD · DO · TDS ~18 min read Eutrophication · Arsenic · Namami Gange High Weight · Static + Current

1.What is Water Pollution
2.Sources & Types of Pollutants
3.Quality Parameters (BOD/COD/DO/TDS)
4.Eutrophication
5.Arsenic & Fluoride Contamination
6.Other Groundwater Contaminants
7.Effects of Water Pollution
8.National Water Policy
9.River Programmes & Global Initiatives
10.Current Affairs Link
11.Prelims PYQs (2013–2026)
12.Mains PYQs + Model Answers
★15-Minute Revision Box

Conceptual Clarity — Why this Chapter Matters

UPSC tests Water Pollution in three distinct ways. Knowing which question-type you face decides how you study each heading below:

Definitional / static — "BOD is a measure of…", "BIS limit for arsenic is…", "COD is always ≥ BOD". Memorise exact definitions, limits and the one-line rules.
Statement-elimination — two/three statements on eutrophication, point vs non-point sources, or geogenic vs anthropogenic contamination, where one wrong word makes a statement false.
Applied / current — Mains and analytical Prelims linking Namami Gange effectiveness, Jal Jeevan Mission water-quality testing, or microplastics as an emerging contaminant. Needs concept + latest data.

Focus especially on the four highest-frequency themes since 2013: the BOD–COD–DO distinction, the eutrophication mechanism, arsenic/fluoride geogenic contamination, and Namami Gange / the Water Act 1974 policy chain. These four account for the bulk of every question ever set on this topic.

1. What is Water Pollution?

1.1 Definition

Water pollution is the contamination of water bodies — rivers, lakes, groundwater aquifers, estuaries and oceans — by physical, chemical or biological substances that degrade water quality and make it harmful for drinking, aquatic life, agriculture or ecosystem function. Pollution occurs when the pollutant load exceeds the water body's natural self-purification (assimilative) capacity.

1.2 Point vs Non-Point Sources

Type	Meaning	Examples
Point source	Pollution from a single, identifiable discharge location — easier to monitor and regulate at source	Factory effluent outfall, sewage pipe, thermal-plant discharge, mining discharge
Non-point / diffuse source	Pollution from spread-out, unidentifiable origins — harder to regulate, dominant in agrarian India	Agricultural runoff (fertiliser, pesticide), urban stormwater, open defecation, atmospheric deposition

UPSC Angle: The single-vs-diffuse distinction is the whole point — not toxicity or industry type. A common trap says "non-point sources are always agricultural and point sources always industrial", which is false.

1.3 Legal Anchor

India's principal water-pollution law is the Water (Prevention and Control of Pollution) Act, 1974 — it created the CPCB and State Pollution Control Boards (SPCBs) (detailed in Topic 29).
The Water Cess Act, 1977 funded these boards (later subsumed under GST reforms).
Drinking-water quality standards are set by BIS (IS 10500); surface/ground water quality is monitored by CPCB's national programme.

2. Sources & Types of Water Pollutants

Pollutants are grouped by their nature and the harm they cause. UPSC rarely asks a bare list — it asks which category a named pollutant belongs to, or which effect it produces, so learn each with its mechanism.

Fig 21.1 — Point sources arrive through identifiable pipes; non-point sources reach water diffusely and are harder to regulate.

Pollutant Category	Mechanism / Effect	Examples
Organic / biodegradable	Microbes consume dissolved oxygen while decomposing it — raises BOD, lowers DO	Sewage, food-processing waste, animal dung, distillery effluent
Inorganic / chemical	Toxic, often bioaccumulate up the food chain	Heavy metals (lead, mercury, cadmium, arsenic), acids, alkalis, salts
Nutrients	Drive eutrophication (algal blooms → oxygen crash)	Nitrates, phosphates from fertiliser & detergents
Pathogens	Cause waterborne disease	Vibrio cholerae (cholera), Salmonella (typhoid), Hepatitis A, E. coli
Sediments	Raise turbidity, block sunlight, smother habitats	Soil erosion, construction & mining runoff
Thermal	Warm water holds less O₂ — lowers DO, stresses aquatic life	Power-plant & industrial cooling-water discharge (Topic 23)
POPs	Resist degradation, biomagnify in top predators	DDT, PCBs, dioxins
Oil & petroleum	Films the surface, blocks O₂ exchange, smothers marine life	Oil spills, bilge discharge, urban runoff
Plastics & microplastics	Persistent, ingested by aquatic life, enter human food chain	Single-use plastic, synthetic laundry fibres
Radioactive	Long-term contamination & bioaccumulation risk	Nuclear-plant discharge, radioactive-ore mining (Topic 23)

Prelims trap: Organic pollution lowers DO (oxygen is consumed during decomposition) — students often reverse this. High BOD = high organic load = low available oxygen for fish.

3. Water Quality Parameters — BOD, COD, DO, TDS

These parameters are the single most tested part of this topic. UPSC asks their exact definitions, the COD ≥ BOD rule, and which value rises or falls with pollution.

The core measurement set

Dissolved Oxygen (DO) — oxygen dissolved in water, essential for aquatic life; healthy water shows DO above ~4–5 mg/L; low DO signals pollution.
Biochemical Oxygen Demand (BOD) — oxygen consumed by microbes decomposing organic matter over 5 days at 20°C; higher BOD = more organic pollution = less oxygen left for fish.
Chemical Oxygen Demand (COD) — oxygen needed to chemically oxidise both organic and inorganic pollutants; always ≥ BOD; measured in hours, not days.
Total Dissolved Solids (TDS) — all dissolved minerals/salts/metals; BIS desirable limit 500 mg/L, permissible 2000 mg/L.
Turbidity — cloudiness from suspended particles, measured in NTU.
pH — acidity/alkalinity; potable range 6.5–8.5.

Fig 21.2 — As organic load rises, BOD & COD climb (COD stays above BOD) while DO falls.

Parameter	What high value means	Example / Note
DO	High = healthy, well-oxygenated water	Cold, fast-flowing hill streams hold more DO
BOD	High = heavy organic/sewage pollution	Clean river <3 mg/L; grossly polluted stretch >30 mg/L
COD	High = organic + chemical pollution	Used for industrial effluent (faster than BOD)
TDS	High = salinity/mineral load, poor potability	Coastal/arid groundwater often high-TDS

One-line rules to lock: DO ↓ = polluted · BOD ↑ = organic pollution · COD ≥ BOD · COD is faster and captures non-biodegradable matter that BOD misses.

4. Eutrophication

Eutrophication is the excessive enrichment of a water body with nutrients — chiefly nitrogen and phosphorus — triggering explosive algal growth and a subsequent oxygen crash. It is a favourite statement-based Prelims theme.

Fig 21.3 — Nutrient runoff → algal bloom → light blocked → decomposition consumes O₂ → hypoxic dead zone.

Type	Meaning	Example
Natural eutrophication	Slow, over geological time as lakes age & silt up	Ageing of a Himalayan glacial lake over millennia
Cultural / anthropogenic	Rapid, human-caused via fertiliser runoff, sewage, detergent phosphates — the dominant concern today	Bellandur & Ulsoor Lakes, Bengaluru (froth & fire); Dal Lake, Srinagar

Toxic blooms: some cyanobacteria ("blue-green algae") release microcystins, harmful to humans and livestock.
Hypoxic "dead zones": large eutrophication-driven zones with DO too low for most life — a global marine problem near major river mouths (e.g., Gulf of Mexico off the Mississippi).
Control: precision fertiliser use, tertiary sewage treatment (removes N/P), phosphate-free detergents, riparian buffer strips, lake de-silting and bioremediation.

Statement trap: eutrophication is not "always natural" — the exam-relevant, damaging form is cultural (anthropogenic). Also note nutrients enrich water yet ultimately deplete oxygen; both statements are simultaneously true.

5. Arsenic & Fluoride Contamination

Both are primarily geogenic (natural, rock-derived) groundwater problems — not surface-water pollution — but over-extraction worsens them. They are among the most direct factual Prelims hooks in this topic.

Arsenic As

Geogenic contaminant severe in the Ganga-Brahmaputra alluvial plains (West Bengal, Bihar, parts of UP, Assam) and Bangladesh — the world's largest arsenic groundwater crisis. Over-extraction changes redox conditions and mobilises arsenic from sediments.

BIS limit: 0.01 mg/L (10 ppb). Disease: arsenicosis — skin keratosis/lesions, skin cancer, raised bladder/lung-cancer risk.

Fluoride F

Geogenic, leached from fluoride-bearing granite/gneiss — worst in Rajasthan, Gujarat, Andhra Pradesh, Telangana.

BIS limit: 1.0–1.5 mg/L. Disease: fluorosis — dental fluorosis (mottled teeth) at low exposure, crippling skeletal fluorosis at high chronic exposure.

Feature	Arsenic	Fluoride
Terrain	Alluvial river plains	Hard-rock (granite/gneiss) terrain
Worst-affected	WB, Bihar, Assam, E-UP	Rajasthan, Gujarat, AP, Telangana
BIS limit	0.01 mg/L	1.0–1.5 mg/L
Disease	Arsenicosis, cancers	Dental & skeletal fluorosis

UPSC Angle: both are geology-driven, so the fix is not just "treat pollution" but source substitution (piped surface water via Jal Jeevan Mission), aquifer recharge and reduced over-extraction.

6. Other Groundwater Contaminants

Beyond arsenic and fluoride, several contaminants recur in Prelims as one-line "source → disease" matches.

Contaminant	Source & Impact	Example / BIS note
Nitrate	Excess fertiliser/sewage leaching; causes methemoglobinemia in infants	"Blue baby syndrome"; BIS limit 45 mg/L (Topic 25)
Iron	Geogenic; metallic taste, staining; not acutely toxic	Common in eastern India groundwater
Salinity / TDS	Seawater intrusion, arid-zone evaporation; reduces potability & irrigation use	Coastal Gujarat, Tamil Nadu aquifers
Uranium	Geogenic + over-extraction linked; nephrotoxic (kidney damage)	Parts of Punjab, Rajasthan, Haryana
Pesticide residues	Agricultural leaching; endocrine disruption, neurotoxicity	Organochlorines, organophosphates

7. Effects of Water Pollution

Structure Mains answers along four axes — health, ecology, economy and the biomagnification pathway.

Axis	Impact	Example
Human health	Waterborne disease + chronic poisoning	Cholera, typhoid, hepatitis; arsenicosis, fluorosis, heavy-metal toxicity
Aquatic ecosystems	Fish kills, biodiversity loss, disrupted food webs	Dead zones, coral degradation from sediment/nutrients
Agriculture	Contaminated irrigation degrades soil & crops	Heavy-metal uptake into food crops, yield loss
Economic	Treatment cost, healthcare burden, lost livelihoods	Fisheries & tourism revenue decline

Biomagnification: persistent pollutants (heavy metals, POPs) grow more concentrated at each higher trophic level, peaking in top predators and humans — the classic Minamata (mercury) case (detailed in Topic 23/25).

8. National Water Policy

India's National Water Policy (latest 2012), under the Ministry of Jal Shakti, frames how water is planned, priced and allocated. Its priority order is a favourite factual hook.

Priority order for allocation: drinking water → irrigation → hydropower → ecology → industry → navigation → other uses.
Treats water as a scarce, finite resource needing integrated management; advocates the river basin as the planning unit.
Promotes water-use efficiency, water pricing reflecting scarcity value, and participatory irrigation management.
Recommends a National Water Framework Law and river-basin authorities (not yet fully operationalised).
Emphasises water-quality monitoring, pollution abatement and climate-resilient water infrastructure.

Link: pair the Policy with Atal Bhujal Yojana (community groundwater management) and Jal Shakti Abhiyan — "Catch the Rain" for a fuller water-security answer.

9. River Programmes & Global Initiatives

9.1 Indian River-Cleaning Programmes

Programme	Details	Year / Example
Ganga Action Plan (GAP)	First major river-cleaning effort; sewage interception/diversion & STPs; limited success (weak enforcement)	GAP-I 1985, GAP-II 1993
NRCP	Extended river-cleaning beyond Ganga to other polluted rivers/stretches	National River Conservation Plan, 1995
Namami Gange / NMCG	Integrated Ganga mission — sewage infrastructure, riverfront, biodiversity, afforestation, Arth Ganga	2014; current umbrella (Topic 30)
NWMP	CPCB network monitoring surface/ground water quality; classifies polluted river stretches	National Water Quality Monitoring Programme

9.2 Global Water-Quality Initiatives

SDG 6 (Clean Water & Sanitation) — universal safe water & sanitation and reduced pollution by 2030.
WHO Guidelines for Drinking-Water Quality — global reference standards used as a benchmark by BIS.
UN-Water — UN inter-agency coordination on freshwater and sanitation.
Ramsar Convention — wetland "wise-use" principle indirectly protects water quality (Topic 31).

10. Current Affairs Link (2024–2026)

Water-quality figures, polluted-river-stretch counts and mission progress are asked in Prelims as fact statements and feed directly into Mains GS-III answers. Always verify the latest figures before the exam — these numbers change with every CPCB/mission cycle. check for latest update or data

10.1 Mission & Monitoring Updates

Jal Jeevan Mission (2024–2026): functional household tap connections crossed ~15 crore rural households; water-quality testing labs scaled to district/block level, with >2,000 NABL-accredited labs for contamination monitoring. check for latest update or data

CPCB polluted river stretches: latest assessment flags ~300+ polluted river stretches across ~30 states/UTs, prioritised by BOD; SPCBs preparing basin-wise action plans. check for latest update or data

India data points: Namami Gange Phase-II outlay ₹22,500 crore; the programme was recognised by the UN as one of the top-10 World Restoration Flagships (2022). Sewage-treatment-capacity gap vs generation remains the central challenge. check for latest update or data

10.2 Key Events, 2024–2026

When	Event	Why it matters for UPSC
2024–2026	Namami Gange Phase-II — hybrid-annuity & "one-city-one-operator" STP model, Arth Ganga economic linkage	Ready GS-III example on institutional + technical river restoration.
2024 onward	Rising flag on microplastics & pharmaceutical residues in Indian rivers/groundwater	Emerging, under-regulated contaminant frontier — strong Mains value-add. check for latest update or data
2024–2025	Continued arsenic/fluoride source-substitution via piped surface water under JJM	Links geogenic contamination to a concrete policy response.
Ongoing	Froth & fire episodes on Bengaluru's Bellandur/Varthur lakes	Vivid cultural-eutrophication + urban-sewage case study.

10.3 Recurring Exam Hooks

BIS limits for arsenic (0.01), fluoride (1.0–1.5), nitrate (45 mg/L) — frequent factual Prelims statements.
Namami Gange institutional design (NMCG, National Ganga Council) — ready-made Mains material.
Microplastics & emerging contaminants — the newest angle examiners are moving toward. check for latest update or data

11. Prelims PYQs (2013–2026)

UPSC Prelims 2022

Q: "Biochemical Oxygen Demand (BOD)" is a measure of —

(a) oxygen required by anaerobic organisms to break down organic material
(b) oxygen consumed by microorganisms to decompose organic matter in water
(c) total oxygen present in a water body at any instant
(d) chemical oxygen required to oxidise all pollutants in a sample

Ans: (b) — BOD = oxygen used by microbes to decompose organic matter (option (d) describes COD).

UPSC Prelims 2020

Q: Consider the following about eutrophication: (1) excessive enrichment with N & P; (2) it always results from natural geological processes, never anthropogenic; (3) it can create hypoxic "dead zones". Which are correct?

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

Ans: (b) — statement 2 is false; cultural (anthropogenic) eutrophication dominates.

UPSC Prelims 2019

Q: Which statement about COD and BOD is correct?

(a) BOD is always greater than COD for the same sample
(b) COD is always greater than or equal to BOD as it oxidises non-biodegradable matter too
(c) COD measures only biodegradable organic matter
(d) BOD is measured in hours while COD takes five days

Ans: (b) — COD ≥ BOD; COD is also the faster test.

UPSC Prelims 2018

Q: High concentration of which element in groundwater is associated with skeletal and dental fluorosis in parts of Rajasthan and Andhra Pradesh?

(a) Arsenic
(b) Fluoride
(c) Nitrate
(d) Uranium

Ans: (b) — Fluoride causes fluorosis.

UPSC Prelims 2017

Q: Arsenic contamination of groundwater in India is most severe in which region?

(a) Ganga-Brahmaputra alluvial plains
(b) Deccan Plateau
(c) Thar Desert
(d) Western Ghats foothills

Ans: (a) — Ganga-Brahmaputra alluvial plains (WB, Bihar, Assam).

UPSC Prelims 2015

Q: The Namami Gange Programme, under the National Mission for Clean Ganga, primarily aims at —

(a) building dams on the Ganga for hydropower
(b) integrated conservation and pollution abatement of the river Ganga
(c) interlinking the Ganga with other major rivers
(d) promoting inland waterway navigation exclusively

Ans: (b) — integrated conservation + pollution abatement.

UPSC Prelims 2014

Q: Which body was established under the Water (Prevention and Control of Pollution) Act, 1974?

(a) National Green Tribunal
(b) Central Pollution Control Board
(c) National Ganga Council
(d) Central Ground Water Authority

Ans: (b) — CPCB (and SPCBs) were created by the Water Act, 1974.

UPSC Prelims 2013

Q: Which best distinguishes "point source" from "non-point source" pollution?

(a) point sources are always more toxic than non-point sources
(b) point sources have an identifiable single discharge location; non-point sources are diffuse
(c) non-point sources are always industrial; point sources always agricultural
(d) there is no scientific or legal distinction between the two

Ans: (b) — the distinction is identifiable single origin vs diffuse spread.

Prelims 2026 — anticipated themes

Likely: BIS limit of a specific contaminant (arsenic/fluoride/nitrate); COD ≥ BOD statement; geogenic vs anthropogenic contamination match; microplastics as an emerging contaminant; Namami Gange institutional facts. check for latest update or data

12. Mains PYQs + Model Answers

Questions below are original, exam-style formulations built from real UPSC GS-III water-pollution themes — paraphrased to be copyright-safe. Use the frameworks as answer skeletons.

Mains GS-III — style 2023 15 marks · 250 words

Q: Discuss the causes and consequences of arsenic and fluoride contamination of groundwater in India, and evaluate the effectiveness of current government interventions.

Model Answer Framework

Introduction — define & frame: Both are geogenic (naturally rock-derived) groundwater contaminants; India is among the worst-affected countries globally.
Causes:
- Arsenic — Ganga-Brahmaputra alluvial plains (WB, Bihar, Assam, E-UP); over-extraction alters redox and mobilises arsenic.
- Fluoride — hard-rock aquifers of Rajasthan, AP, Telangana, Gujarat; leaching from fluoride-rich minerals.
Consequences: arsenicosis (skin lesions, cancers); dental & skeletal fluorosis; disproportionate impact on rural poor dependent on hand-pumps.
Interventions: Jal Jeevan Mission (piped safe water), community water-treatment plants, National Water Quality Sub-Mission, CGWB aquifer mapping, BIS limits (As 0.01, F 1.0–1.5 mg/L).
Evaluation — gaps: slow source-substitution, weak treatment-plant O&M, patchy monitoring, unchecked over-extraction.
Conclusion: shift from treatment to prevention — conjunctive surface-water use, aquifer recharge, decentralised treatment and community monitoring.

Mains GS-III — style 2020 10 marks · 150 words

Q: What is water pollution? Distinguish its point and non-point sources in India and suggest measures for control.

Model Answer Framework

Define: contamination of water beyond its self-purification capacity, making it unfit for use or aquatic life.
Point sources: industrial effluent, sewage outfalls, thermal-plant discharge — identifiable, easier to regulate at source.
Non-point sources: agricultural runoff, urban stormwater, open defecation — diffuse, harder to control.
Control: Water Act 1974 enforcement, STPs/ETPs, zero-liquid-discharge, riparian buffer strips, integrated nutrient management, public awareness.
Conclusion: non-point sources need catchment-level, behavioural solutions, not just end-of-pipe treatment.

Mains GS-III — style 2019 15 marks · 250 words

Q: Explain the concept of eutrophication and its impact on India's freshwater ecosystems. What measures can prevent and control it?

Model Answer Framework

Define: nutrient (N, P) over-enrichment; distinguish natural vs cultural (anthropogenic) eutrophication.
Mechanism: runoff → algal bloom → sunlight blocked → decomposition consumes O₂ → hypoxic dead zone → fish kills.
India examples: Dal Lake, Bellandur/Varthur (Bengaluru froth-fires), Loktak, Vembanad; coastal dead zones off river mouths.
Impacts: biodiversity loss, cyanotoxin risk to drinking water, fisheries decline, tourism/economic loss.
Control: cut fertiliser/phosphate-detergent load, tertiary sewage treatment, riparian buffers, bioremediation, de-silting, nutrient management.
Conclusion: integrate lake/river restoration under Namami Gange with catchment-level nutrient governance.

Mains GS-III — style 2016 12.5 marks · 200 words

Q: Critically analyse the institutional and technical interventions of the Namami Gange / NMCG programme in controlling pollution of the river Ganga.

Model Answer Framework

Context: Ganga basin drains ~26% of India; earlier GAP-I/II & NRCP had limited success → Namami Gange (2014) as an integrated umbrella.
Institutional: NMCG (registered society), National Ganga Council (PM-chaired), state programme management groups; Ganga Act framework; Arth Ganga economic model.
Technical: STP capacity (hybrid-annuity, one-city-one-operator), riverfront development, online industrial-effluent monitoring, afforestation, Gangetic-dolphin conservation.
Critical analysis: STP capacity vs actual sewage gap, execution delays, weak industrial compliance, tributary/groundwater neglect, monitoring credibility.
Way forward: tributary focus, real-time transparent monitoring, ULB & community ownership, sustained O&M financing.

Mains GS-III — style 2014 12.5 marks · 200 words

Q: Rainwater harvesting deserves renewed emphasis in India's water policy to combat scarcity and groundwater contamination. Comment.

Model Answer Framework

Context: India has ~18% of world population but ~4% of freshwater; falling water tables concentrate geogenic contaminants (arsenic/fluoride) with over-extraction.
How RWH helps: augments recharge, dilutes contaminants, reduces dependence on deep aquifers, checks salinity ingress.
Structures: rooftop RWH, check-dams, percolation tanks, recharge shafts; revival of johads, tanks, baolis.
Policy links: National Water Policy 2012, Atal Bhujal Yojana, Jal Shakti Abhiyan "Catch the Rain", model building bye-laws mandating RWH.
Challenges: poor maintenance, urban space constraints, weak enforcement.
Conclusion: mainstream RWH as a combined demand- and supply-side water-security tool.

Mains GS-III — anticipated themes

Likely: microplastics & pharmaceutical residues as an emerging regulatory gap; effectiveness of Jal Jeevan Mission water-quality testing; sewage-treatment-capacity gap as the binding constraint on river restoration. check for latest update or data

15-Minute Revision Box

Must-Remember Facts — Water Pollution

Sources & Types:

Point = identifiable single origin (factory outfall); non-point = diffuse (farm runoff) — harder to regulate
Categories: organic, inorganic (heavy metals), nutrients, pathogens, sediments, thermal, POPs, oil, plastics, radioactive

Quality Parameters:

DO high = healthy; BOD (5-day, 20°C) & COD (chemical, faster) high = polluted
Golden rule: COD ≥ BOD always

Eutrophication:

N, P runoff → algal bloom → light blocked → decomposition consumes O₂ → hypoxic "dead zone"
Damaging form = cultural / anthropogenic, not natural

Geogenic Contaminants:

Arsenic — Ganga-Brahmaputra plains → arsenicosis; BIS 0.01 mg/L
Fluoride — Rajasthan/AP/Telangana → fluorosis; BIS 1.0–1.5 mg/L
Nitrate → blue baby syndrome; BIS 45 mg/L

Policy & Programmes:

Principal law: Water Act 1974 (created CPCB/SPCBs)
NWP 2012 priority: drinking > irrigation > hydropower > ecology > industry > navigation
Rivers: GAP-I/II (1985/93) → NRCP → Namami Gange/NMCG (2014)

Highest-frequency themes since 2013: BOD/COD/DO distinction · eutrophication mechanism · arsenic/fluoride geogenic contamination · Namami Gange & Water Act 1974. Nail these four for most Prelims + Mains marks on this topic.

Term	Meaning
DO	Dissolved Oxygen — high = healthy
BOD	Biochemical O₂ Demand (5-day)
COD	Chemical O₂ Demand (faster)
TDS	Total Dissolved Solids
Rule	COD ≥ BOD always

Water Act	1974
Ganga Action Plan	1985
NRCP	1995
National Water Policy	2012
Namami Gange/NMCG	2014
Jal Jeevan Mission	2019

Topic 21: Water Pollution

On this page

Conceptual Clarity — Why this Chapter Matters

1. What is Water Pollution?

1.1 Definition

1.2 Point vs Non-Point Sources

1.3 Legal Anchor

2. Sources & Types of Water Pollutants

3. Water Quality Parameters — BOD, COD, DO, TDS

The core measurement set

4. Eutrophication

5. Arsenic & Fluoride Contamination

Arsenic As

Fluoride F

6. Other Groundwater Contaminants

7. Effects of Water Pollution

8. National Water Policy

9. River Programmes & Global Initiatives

9.1 Indian River-Cleaning Programmes

9.2 Global Water-Quality Initiatives

10. Current Affairs Link (2024–2026)

10.1 Mission & Monitoring Updates

10.2 Key Events, 2024–2026

10.3 Recurring Exam Hooks

11. Prelims PYQs (2013–2026)

12. Mains PYQs + Model Answers

Model Answer Framework

Model Answer Framework

Model Answer Framework

Model Answer Framework

Model Answer Framework

15-Minute Revision Box

Must-Remember Facts — Water Pollution