Every Drop Counts: Water Pollution and Conservation

Water pollution is the contamination of water by undesirable substances, organic, inorganic, biological, radiological or thermal, that make it unsafe for drinking, farming, industry or aquatic life. India holds about 18% of the world's people but only 4% of its freshwater, and its rivers, lakes and aquifers are simultaneously overused and under-protected. For UPSC, this theme sits at the junction of environment, governance and rights: the science of pollution, the economics of scarcity, and the law that is now being rewritten to fix both.

A country running dry: India's freshwater crisis

India's freshwater crisis is a mismatch between people and water. Per capita availability has fallen to about 1,486 cubic metres (2021), already below the 1,700 cubic metre stress threshold, and is projected to drop to about 1,367 cubic metres by 2031 (Central Water Commission), deep into scarcity territory. NITI Aayog has projected that demand could double available supply by 2030, and nearly 600 million Indians face high to extreme water stress.

The crisis has three engines. First, groundwater over-extraction: India is the world's largest groundwater user, drawing more than a quarter of the global total, and falling water tables in states like Punjab and Haryana are now regarded as partly irreversible because aquifer compaction permanently destroys storage capacity. Second, contamination: about 70% of groundwater is affected by fluoride, arsenic, nitrate or uranium in affected pockets, with arsenic breaching the 10 ppb limit in parts of West Bengal and Bihar and nitrate affecting an estimated 40 million people. Third, policy distortion: free or heavily subsidised electricity for farm pumps encourages round-the-clock pumping of water-intensive paddy in regions that cannot sustain it.

The human cost is stark. The erstwhile Composite Water Management Index flagged that some 200,000 Indians die every year from unsafe water, and the burden falls hardest on women, who do most water collection, and on Dalit households, which still face restricted access to common sources in parts of rural India. Jal Jeevan Mission, launched in 2019 to give every rural household a tap connection, raised coverage from 17% to over 81% of households by 2026, but functionality audits show that a connection on paper does not always mean safe water on tap, which is why its second phase runs to 2028 with assured service delivery as the goal.

What pollutes India's water

Pollution reaches water through two routes. A point source is a single identifiable discharge point, such as a factory drain or a sewage outfall, which can be monitored and regulated. A non-point source is diffuse, such as fertiliser runoff from thousands of farms or plastic litter washed off city streets, which is far harder to control. India's problem is that both are severe at once.

Municipal sewage is the largest volumetric polluter. Of roughly 72,368 MLD of sewage generated in urban India, only about 28% is actually treated; the rest, over 52,000 MLD, flows untreated into rivers, lakes and the sea. Industrial effluents add heavy metals, dyes and toxic chemicals: tanneries, textiles, chemicals and pharmaceuticals discharge into rivers like the Ganga and Yamuna despite decades of regulation. Agricultural runoff carries excess nitrogen and phosphorus into water bodies, triggering eutrophication, the explosive growth of algae that blocks sunlight and, on decay, strips water of oxygen.

Two scientific yardsticks matter here. Biochemical Oxygen Demand (BOD) is the oxygen that microbes need to break down organic matter in water: a high BOD means heavy organic pollution. Dissolved oxygen (DO) is the oxygen actually available in water for fish and aquatic life: when BOD soars, DO crashes and fish die. Biomonitoring in 2024-25 rated the Ganga-Yamuna's biological water quality from 'Good' to 'Moderate', a genuine recovery signal after years of 'Poor' ratings.

Below the surface, groundwater contamination is a slower disaster. Arsenic in the Bengal basin, fluoride in Rajasthan and Andhra Pradesh, nitrate from fertiliser leaching, and uranium traces in parts of Punjab and Delhi's periphery make aquifers unsafe even where water tables hold. Over-pumping worsens the chemistry: as fresh water is drawn down, deeper, mineral-heavy layers and even seawater intrude into the aquifer.

Reading a water test: six parameters that decide safety

Pollution debates talk in numbers that prelims loves. Six parameters decide almost every official verdict on whether water is fit to drink, bathe in, or support fish:

Note the division of labour. BOD, COD and DO describe the organic and oxygen balance of a river, the language of the Ganga clean-up; coliform describes biological safety, the language of drinking water; TDS and pH describe chemical acceptability. A stretch can pass one test and fail another, which is why a river can be declared fit for bathing while its water remains undrinkable without treatment.

The law catches up: the Water Act and its 2024 amendment

The Water (Prevention and Control of Pollution) Act, 1974 is India's first major environmental statute. It created the Central Pollution Control Board (CPCB) and the State Pollution Control Boards (SPCBs), made their prior consent mandatory for any industry likely to discharge sewage or effluent, and punished violations with imprisonment. For fifty years its weakness was enforcement: criminal prosecution moved slowly, penalties were tiny, and consent conditions were weakly monitored.

The Water (Prevention and Control of Pollution) Amendment Act, 2024 rewrites the enforcement logic. Its headline move is decriminalisation: most violations that earlier carried 1.5 to 6 years of imprisonment now attract graded civil penalties of Rs 10,000 to Rs 15 lakh, with an additional Rs 10,000 per day for continuing contraventions. Imprisonment survives mainly for operating without consent and for failing to pay penalties. The philosophy mirrors the Jan Vishwas Act, 2023: treat minor lapses as civil wrongs so that enforcement is swift and certain rather than rare and severe.

An adjudicating officer, of at least Joint Secretary rank at the Centre or Secretary rank in a state, now holds inquiries and fixes penalties, replacing slow court trials. Appeals lie to the National Green Tribunal (NGT) after depositing 10% of the penalty, and collections flow into the Environment Protection Fund under the Environment (Protection) Act, 1986. The Centre also gains powers to prescribe how SPCB chairpersons are appointed and to exempt certain low-polluting industrial categories from consent, an ease-of-doing-business push. Government departments are not spared: a violating department's head pays a penalty equal to one month's basic salary unless due diligence is proved.

The trade-offs are the real mains fodder. Fines of Rs 15 lakh are negligible for a large polluter, so deterrence may weaken unless penalties are turnover-linked. Central control over SPCB appointments touches the federal nerve, since water is a State subject. And consent exemptions, however well-intentioned, need real-time effluent monitoring, or 'white category' industries become blind spots. The amendment initially applies to Himachal Pradesh, Rajasthan and the Union Territories; other states adopt it by resolution.

Fly ash: India's largest industrial solid waste

Fly ash is the fine, powdery residue left when coal is burnt in thermal power plants, carried up with flue gases and captured by electrostatic precipitators. Because India generates most of its electricity from coal, fly ash is the country's largest industrial solid waste stream by volume, accumulating in vast ash ponds and dykes around power stations. Unmanaged ash leaches heavy metals into groundwater, its fine particles blow into surrounding habitations and fields, and dyke breaches have flooded villages with ash slurry, which is why fly ash is as much a water and land problem as an air one.

The policy answer is utilisation, not just disposal. Fly ash is a proven raw material: it goes into bricks and blocks, into Portland pozzolana cement as a partial replacement for clinker, into road and flyover embankments, into mine backfilling, and, within prescribed limits, as a soil amendment in agriculture. The regulatory push came through the 2021 fly ash utilisation notification, which set a phased roadmap toward 100 per cent utilisation of ash generated by thermal power plants, with penalties for non-compliance and defined end-uses that plants must achieve. For mains, fly ash is the textbook case of industrial symbiosis, one industry's waste becoming another's raw material, and of how a notification converts a liability into a resource when enforcement follows.

Cleaning the Ganga: Namami Gange

Namami Gange is the Union Government's flagship river-cleanup programme, launched in June 2014 after the Ganga Action Plans of 1986 and 1993 spent barely Rs 4,000 crore over 30 years with fragmented results. Implemented by the National Mission for Clean Ganga (NMCG), it began with a Rs 20,000 crore outlay and was extended through Namami Gange Mission-II with Rs 22,500 crore up to March 2026, taking cumulative spending past Rs 42,000 crore.

The programme's spine is sewage infrastructure: 513 projects worth Rs 42,019 crore were sanctioned, of which 344 were complete by late 2025, including 138 sewage treatment plants with 3,806 MLD of operational capacity out of 216 sanctioned sewerage projects. Arth Ganga adds an economic layer, riverfront development, floating markets, ferry services and natural farming along a 10-km riverbank stretch, so the river's economy rewards its protection rather than its exploitation.

Results are measurable but partial. BOD in Uttar Pradesh's Ganga stretch fell from 10-20 mg/l in 2015 to 3-6 mg/l in 2022, and 2024-25 biomonitoring found 'Good' to 'Moderate' biological water quality, with the return of the Gangetic dolphin, India's national aquatic animal, as a living indicator. Yet most urban sewage still goes untreated, fund releases lag sanctions, and centre-state coordination gaps persist. The 2015 mains question asked what 'quantum leaps' could succeed where incremental inputs failed: the honest answer is complete sewage interception, decentralised treatment, ecological flows, and making treated wastewater a priced resource rather than a waste.

Ecological flow, or e-flow, deserves a definition: it is the minimum natural flow a river needs to sustain its ecosystems, fisheries and self-purification. Dams, barrages and over-extraction on the Ganga disrupt e-flows, and no treatment plant can compensate for a river that has too little water to dilute what remains.

Beyond rivers: marine and oil pollution

Marine pollution is the contamination of oceans by chemicals, waste and plastics, most of it originating on land and reaching the sea through rivers and drains. About 11 million tonnes of plastic enter the oceans every year (UNEP), making up about 80% of marine debris, and the World Economic Forum (2016) warned of more plastic than fish in the sea by 2050 on current trends. Excess nutrients from sewage and fertilisers create dead zones, oxygen-starved patches where marine life cannot survive, while pollutants like mercury biomagnify, growing more concentrated at each step of the food chain from plankton to predatory fish to humans.

India's coastal defences rest on international and domestic law. MARPOL (1973/78) is the global treaty regulating ship-source pollution, oil, chemicals, sewage and garbage, which India enforces through maritime rules such as the Merchant Shipping Rules, 2009. The High Seas Treaty (BBNJ Agreement), 2023 is the first treaty protecting biodiversity beyond national jurisdiction, enabling high-seas marine protected areas. India banned identified single-use plastic items from 1 July 2022 and runs Extended Producer Responsibility for plastic packaging under the Plastic Waste Management Rules.

Oil pollution, the release of petroleum into marine and coastal ecosystems, is among the most destructive forms: it smothers intertidal life, poisons seabirds and disrupts fisheries for years. The good news is structural: large tanker-spill frequency has fallen over 90% since the 1970s, to about two a year in the 2020s, thanks to double-hull mandates and better traffic management. India's reminders include the 2017 Ennore (Chennai) spill from the Dawn Kanchipuram-BW Maple ship collision, which showed how slow containment response multiplies damage.

Three more treaties complete the marine rulebook. The London Convention (1972) is the global pact against dumping wastes at sea: it restricts the dumping of oil, radioactive waste and heavy metals, allows only designated and monitored dumping zones with mandatory impact assessments, and requires prior notification for transboundary activities. The OPRC (1990), the International Convention on Oil Pollution Preparedness, Response and Cooperation, is the framework for oil-spill preparedness and joint response. The Global Plastics Treaty, mandated by UNEA Resolution 5/14, is still under negotiation and aims at a legally binding instrument covering the full plastics lifecycle. At home, the National Oil Spill Disaster Contingency Plan (NOS-DCP), led by the Indian Coast Guard, assigns roles and response strategies for oil-spill emergencies in Indian waters.

Dead zones and a souring ocean

Dead zones are coastal areas where oxygen falls so low (a state called hypoxia) that most marine life suffocates or flees. The mechanism runs through the farm belt: nitrogen and phosphorus washed off fields and out of drains feed algal blooms, the blooms die and decompose, and decomposition consumes the oxygen. Hundreds of coastal dead zones are now mapped worldwide, including seasonally oxygen-starved patches in the northern Indian Ocean.

Ocean acidification is the slower chemical twin. The oceans have absorbed roughly a quarter to a third of humanity's carbon dioxide emissions, and surface ocean acidity has risen by about 30 percent since the industrial era. The cost falls on calcifying life: corals build skeletons more slowly, shellfish larvae fail, and the reef and shellfish economies discussed in the mangroves and coral reefs article absorb the damage. Unlike an oil spill, no boom or skimmer can collect a pH change.

Treating water as wealth: trading and reuse

Only about 28% of India's sewage is treated, and barely 3% of that is beneficially reused: the rest is a wasted asset. Water trading is a market-based mechanism that treats water, or treated wastewater, as a tradable commodity so that it flows to its most productive use. The operative Indian instrument is the Water Reuse Certificate (WRC), a tradable, carbon-credit-style permit developed with the World Bank-hosted 2030 Water Resources Group: a regulator sets reuse targets, users who exceed them earn certificates, and laggards buy certificates instead of defaulting.

The model is already moving. Maharashtra's water regulator, MWRRA, mandates 20% effluent reuse, a framework endorsed by NITI Aayog. AMRUT 2.0 pushes treated-wastewater reuse in cities, the Swachh Bharat Mission 2.0 targets a 'Water+' rating of 100% wastewater treatment, and models like Chennai's wastewater recycling and the Hindustan Zinc-Udaipur sewage-reuse partnership show effluent becoming an input. The pitfalls are pricing, near-free freshwater makes costlier treated water uncompetitive, storage to balance continuous treatment with fluctuating demand, and weak regulators to enforce mandates.

National Water Policy: from building supply to managing demand

India's National Water Policies of 1987, 2002 and 2012 agreed on allocation priorities, drinking water first, but kept faith with supply-side engineering: more dams, more canals, more borewells. The draft National Water Policy of 2020, prepared by a committee chaired by Mihir Shah, breaks with that instinct in three ways:

• Demand first: crop choices matched to agro-climatic zones, micro-irrigation and industrial recycling come before new supply projects in the sequence.

• One institution: a National Water Commission would merge the Central Water Commission and the Central Ground Water Board, so rivers and the aquifers beneath them are planned as one system.

• Rights with pricing: a lifeline quantity of water as an entitlement for all, volumetric pricing above it, and legally protected flows for nature itself.

The draft remains unadopted, which is itself the mains point: India's water governance is still run by the supply-side machinery the draft wants to retire, and every scheme in this article, from Jal Jeevan Mission to Atal Bhujal Yojana, has to work through that machinery.

Conserving every drop: the groundwater and supply push

Atal Bhujal Yojana (2019) is the community-led answer to the groundwater crisis: it funds village-level groundwater management across 8,220 gram panchayats in seven water-stressed states, linking central money to measured aquifer outcomes rather than just structures built. Jal Shakti Abhiyan: Catch the Rain runs nationwide rainwater-harvesting and recharge campaigns, with its 2025 edition targeting 148 water-stressed districts, while Mission Amrit Sarovar (2022) has revived over 68,000 village water bodies.

Groundwater extraction itself is regulated by the Central Ground Water Authority, constituted under the Environment (Protection) Act, 1986, which requires no-objection certificates for industrial and commercial groundwater users and can order closure of violators.

On the demand side, PMKSY-Per Drop More Crop subsidises drip and sprinkler irrigation to raise water-use efficiency in agriculture, which consumes the lion's share of water, and the National Water Mission targets a 20% improvement in overall water-use efficiency. The controversial supply-side answer is river interlinking, exemplified by the Rs 44,605-crore Ken-Betwa Link: a 77-metre dam and 221-km canal promising drinking water to 62 lakh people and irrigation for 10.62 lakh hectares, but submerging about 9,000 hectares including 4,141 hectares of Panna Tiger Reserve core area and displacing several thousand families. Critics note that groundwater assessments found most Bundelkhand districts in the 'safe' category, suggesting cheaper watershed management could deliver more water per rupee.

The right to water itself rests on judge-made law: in Subhash Kumar v. State of Bihar (1991) the Supreme Court read the right to pollution-free water into Article 21's right to life, and in A.P. Pollution Control Board v. M.V. Nayudu (2000) it held the state constitutionally bound to provide clean drinking water. Without a codified national water-rights law, however, the right remains easier to cite than to claim.

India's oldest water technology is community engineering. Ahar-pynes are the floodwater-harvesting channels and reservoirs of Bihar, johads are the crescent-shaped earthen check dams of Rajasthan that recharge wells, kudimaramath is Tamil Nadu's tradition of community-maintained tank desilting, and stepwells and check dams store monsoon runoff for the dry months. Reviving them alongside modern rainwater harvesting is the cheapest recharge strategy available. On the industrial side, Zero Liquid Discharge (ZLD) is the norm that no effluent leaves the factory gate: wastewater is treated, recycled and reused in a closed loop, now mandated for water-guzzling sectors like distilleries and textiles in critically polluted stretches. The remaining governance gap is the absence of Independent Regulatory Authorities (IRAs) for water in most states, empowered bodies that could set reuse targets, adjudicate disputes and enforce compliance at arm's length from line departments.

Managing water whole: IWRM and the Dublin principles

Integrated Water Resources Management (IWRM) is the doctrine that surface water, groundwater and land use form one system and must be planned together. It rests on the Dublin Principles of 1992: freshwater is finite and vulnerable; water development should be participatory; women play a central role in managing water; and water is an economic good as well as a social one. India's One Water Approach is the same instinct in domestic dress: rain, river, aquifer and treated wastewater administered as a single resource instead of by separate departments that never meet.

Mountains and glaciers: the world's water towers

The 2025 UN World Water Development Report, titled Mountains and Glaciers: Water Towers, estimates that mountain waters supply 55 to 60 percent of global freshwater flows and that about two billion people depend on them. For India the point is strategic: Himalayan snow and ice feed the Indus, Ganga and Brahmaputra through the dry season, making the mountains the country's least governed water asset. Glacier retreat first swells summer flows, then shrinks them, a sequence that dam design, flood planning and inter-state sharing arrangements are barely built for.

When a tech capital queued for tankers: Bengaluru, 2024

In the summer of 2024, Bengaluru faced its worst water crisis in decades. Storage in the Cauvery reservoirs ran near 39 percent of capacity in the dry months, thousands of borewells failed, water tanker prices had to be capped by government order, and residents were fined for using drinking water to wash cars. The causes were built, not meteorological: lake catchments paved over, the historic chain of interconnected tanks broken, and groundwater mined well beyond recharge. The lesson examiners draw is that India's water crisis is as much a land-use and governance failure as a rainfall failure.

The river interlinking debate, with Ken-Betwa as the test case

River interlinking proposes moving water from supposedly surplus basins to deficit ones through a network of link canals; the National Water Development Agency has studied 30 such links since 1982. The Ken-Betwa link, sanctioned at Rs 44,605 crore, is the first actually being built, which makes it the live experiment for the whole idea:

The way forward

The water agenda for the next decade is less about new missions than about making existing ones work. Complete and properly operate sewage treatment capacity, then reuse the treated water for irrigation and industry so discharge into rivers falls structurally. Shift Jal Jeevan Mission from connection-counting to assured, metered, sensor-monitored service delivery. Price freshwater realistically so that Water Reuse Certificates find buyers, regulate extraction in over-exploited blocks, and treat river interlinking as a last resort after local recharge is exhausted. Above all, enforce the amended Water Act's civil penalties swiftly and publicly: the 2024 reform bet everything on speed and certainty over severity, and that bet must now be seen to pay.

Key Terms

• Water pollution: Water pollution is the contamination of rivers, lakes, groundwater and coastal waters by sewage, industrial effluents, agricultural runoff, plastics and other pollutants, making water unsafe for drinking, irrigation and aquatic life. Its main indicators include dissolved oxygen, biochemical oxygen demand and the presence of heavy metals and pathogens. In India it is regulated principally through the Water Act of 1974, with the National Mission for Clean Ganga (Namami Gange) as the flagship river rejuvenation programme. Example: Untreated sewage and industrial discharge have made stretches of the Yamuna in Delhi among the most polluted river reaches in the country, with dissolved oxygen near zero.
• freshwater crisis: The growing gap between humanity's demand for freshwater and the reliable supply available, driven by rising consumption, pollution of rivers and aquifers, groundwater over-extraction and climate disruption of rainfall patterns. India is water-stressed, with per capita availability falling steadily and many aquifers, especially in the northwest, being mined faster than they recharge. The crisis links water, food and energy security and is a recurring UPSC theme across environment, geography and governance. Example: Chennai's 2019 Day Zero, when the city's reservoirs ran nearly dry and water had to be brought in by train, a stark illustration of urban freshwater crisis.
• NITI Aayog: NITI Aayog is the Indian government's premier policy think tank, established on 1 January 2015 to replace the Planning Commission. Chaired by the Prime Minister with a Governing Council of all chief ministers, it promotes cooperative federalism, publishes indices like the SDG India Index, and runs programmes such as the Aspirational Districts Programme. It matters for UPSC because questions contrast its bottom-up, advisory role with the Planning Commission's top-down plan allocations. Example: NITI Aayog's SDG India Index, which scores states on sustainable development goals, is a favourite data point in governance answers.
• groundwater over-extraction: Groundwater over-extraction happens when water is pumped out of aquifers faster than rainfall and recharge can replace it, so water tables keep falling year after year. It forces wells to be deepened, raises pumping costs for farmers, and can permanently deplete aquifers in some rock formations. In India, subsidised electricity for agriculture has encouraged excessive pumping in several states. Example: The Central Ground Water Board classifies a large share of blocks in Punjab as over-exploited, meaning annual extraction there exceeds annual recharge.
• contamination: Contamination is the introduction of undesirable substances into water, such as organic chemicals, heavy metals, pathogens or radioactive material, that make it unsafe for drinking, farming, industry or aquatic life. It is the core concept behind water pollution regulation and treatment. Example: Untreated industrial effluents discharging heavy metals into rivers are a major source of water contamination in India.
• policy distortion: Policy distortion refers to government policies, especially subsidies and price controls, that warp the incentives of producers or consumers and cause resource misuse. When a resource is priced far below its real cost, users overconsume it, often damaging the environment in the process. Correcting such distortions is a recurring prescription in water, energy and agriculture policy. Example: Free or heavily subsidised electricity for farm pumps in several Indian states, which encourages round-the-clock groundwater pumping and steadily falling water tables.
• Composite Water Management Index: The Composite Water Management Index (CWMI) is NITI Aayog's index for assessing and ranking states and Union Territories on water management, first released in June 2018. It uses 9 themes and 28 indicators covering groundwater augmentation, restoration of water bodies, irrigation practices, drinking water supply and policy and governance. The index is an exercise in competitive and cooperative federalism, meant to push states to improve water data and governance; it warned that by 2030 India's water demand could be twice the available supply. Example: Gujarat ranked first among general states in the inaugural June 2018 CWMI report, while Jharkhand was the worst performer, a result that has appeared in UPSC and other competitive exams.
• Jal Jeevan Mission: The Jal Jeevan Mission, launched in 2019, aims at Har Ghar Jal: a piped tap-water connection to every rural household, with water-quality testing and community ownership through village water and sanitation committees. It matters for UPSC in drinking-water security, centre-state cost sharing, and the shift from infrastructure creation to assured service delivery. Example: The mission dashboard reporting tap connections to a majority of rural households.
• point source: A point source of pollution is a discharge that comes from a single, identifiable location, such as a factory outlet pipe, a sewage treatment plant or a power station chimney. Because the source is discrete, its pollutant load can be measured, permitted and regulated directly. This contrasts with non-point sources like farm run-off, which are diffuse and much harder to control. Example: An industrial effluent pipe discharging into a river, regulated in India through consent orders under the Water (Prevention and Control of Pollution) Act, 1974.
• non-point source: Non-point source pollution comes from diffuse, scattered origins rather than a single identifiable outlet such as a factory pipe, which makes it harder to monitor and regulate than point-source pollution. Runoff carrying fertilisers, pesticides, and silt from farmland into rivers is the classic case. Controlling it requires landscape-level measures like buffer strips and better farming practices rather than end-of-pipe treatment. Example: Agricultural runoff washing nitrates and phosphates into rivers and lakes, triggering algal blooms and eutrophication.
• Municipal sewage: Municipal sewage is the wastewater collected from households, institutions, and commercial establishments through a city's sewer network, distinct from industrial effluent. It carries organic waste, pathogens, detergents, and nutrients, and when discharged untreated into rivers and lakes it depletes dissolved oxygen and spreads waterborne disease. Treating it in sewage treatment plants (STPs) is the core of urban water-pollution control, and India's large untreated-sewage gap is a key reason rivers like the Ganga remain polluted. Example: Under Namami Gange, hundreds of sewage treatment plants were sanctioned to stop untreated municipal sewage entering the Ganga.
• Industrial effluents: Liquid wastes discharged from industrial processes, containing pollutants such as heavy metals, toxic chemicals, oils and organic matter that degrade water quality when released untreated. They are a major cause of water pollution in India and are regulated under the Water (Prevention and Control of Pollution) Act, 1974 through consent requirements and effluent standards enforced by State Pollution Control Boards. Example: Untreated effluents from tanneries and textile dyeing units have severely polluted rivers and groundwater in several industrial clusters.
• Agricultural runoff: Agricultural runoff is rain or irrigation water that flows off farmland into streams, rivers, lakes, and groundwater, carrying dissolved fertilizers, pesticides, and eroded soil with it. It is a leading cause of non-point source water pollution, driving eutrophication (algal blooms and oxygen depletion) in surface waters and nitrate contamination of aquifers. Managing it is central to sustainable agriculture and the water quality goals of schemes like Namami Gange. Example: Fertilizer runoff from intensive farming in Punjab and Haryana has contributed to high nitrate levels in groundwater across the Green Revolution belt.
• eutrophication: The enrichment of a water body with excess nutrients, chiefly nitrates and phosphates from fertiliser runoff, sewage and industrial effluents. The nutrient surplus triggers algal blooms that block sunlight and, on decay, deplete dissolved oxygen, killing fish and collapsing the aquatic food web. A water body can shift from clear oligotrophic to turbid eutrophic, and in extreme cases to anoxic dead zones. Example: Bengaluru's Bellandur and Varthur lakes, which foam and catch fire from heavy sewage and detergent loads, are well known Indian cases of eutrophication.
• groundwater contamination: Groundwater contamination is the pollution of underground aquifers by chemicals, sewage, industrial effluents, pesticides, or naturally occurring toxins that seep down from the surface. Because aquifers recharge very slowly, contaminated groundwater is extremely difficult and expensive to clean up, and it can poison drinking water for years. It is a serious concern in India, where groundwater provides most irrigation and drinking water. Example: Arsenic contamination of groundwater in West Bengal and fluoride contamination in parts of Rajasthan are well-documented Indian cases.
• Water (Prevention and Control of Pollution) Act, 1974: The Water (Prevention and Control of Pollution) Act, 1974 is India's first major water pollution law, enacted to prevent and control water pollution and to maintain wholesomeness of water. It created the Central Pollution Control Board and the State Pollution Control Boards and made it mandatory for industries to obtain consent from the state boards before discharging sewage or trade effluents. It provides for inspection, sampling, and penalties against polluters, and remains the backbone of India's industrial water regulation. Example: Under this Act, a factory must obtain consent to establish and consent to operate from its State Pollution Control Board before it can legally discharge effluents.
• Water (Prevention and Control of Pollution) Amendment Act, 2024: The Water (Prevention and Control of Pollution) Amendment Act, 2024 modernised the 1974 Act by decriminalising most minor offences, replacing imprisonment with monetary penalties ranging from Rs 10,000 to Rs 15 lakh. It empowers the central government, in consultation with the CPCB, to exempt certain low risk industries from prior consent requirements and to prescribe the nomination process for State Pollution Control Board chairpersons. Adjudicating officers determine penalties, with appeals lying to the National Green Tribunal, reflecting a shift from punishment to compliance oriented regulation. Example: A technical lapse such as delayed consent paperwork, which earlier risked imprisonment, now attracts a monetary penalty under the amended Act, improving ease of doing business while retaining deterrence.
• decriminalisation: In regulatory law, the shift from treating a violation as a criminal offence (punishable with imprisonment) to treating it as a civil wrong punishable with monetary penalties. India's recent environmental reforms use decriminalisation to unclog courts and make compliance proportionate, reserving criminal prosecution for serious or repeated harm. Minor procedural defaults then attract fines adjudicated by officers instead of jail terms. Example: The Biological Diversity (Amendment) Act, 2023 decriminalised most offences under the Act, replacing jail terms with monetary penalties.
• Jan Vishwas Act, 2023: Jan Vishwas Act, 2023 is the punctuated short form of the Jan Vishwas (Amendment of Provisions) Act, 2023, the law that decriminalised 183 provisions across 42 Central Acts administered by 19 ministries. It matters for UPSC as the landmark of trust-based governance replacing criminal punishment for minor business defaults. Example: The Act's replacement of jail terms with adjudicated monetary penalties.
• adjudicating officer: An adjudicating officer is a quasi-judicial authority designated under Indian environmental and economic legislation to inquire into violations and impose civil penalties, replacing criminal prosecution for minor offences. Under the Water (Prevention and Control of Pollution) Amendment Act, 2024, adjudicating officers of at least Joint Secretary rank at the Centre (or Secretary rank in states) hold inquiries and impose penalties ranging from one lakh to fifty lakh rupees for violations that earlier invited up to five years' imprisonment. The mechanism reflects the Jan Vishwas decriminalisation push to make regulatory compliance faster and proportionate. Example: A factory discharging effluent in violation of its consent conditions can now face a monetary penalty from the adjudicating officer instead of a criminal case.
• Environment Protection Fund: The Environment Protection Fund is a fund established under the Environment (Protection) Act, 1986 into which penalties and compensation collected under amended environmental laws are credited. Under the Water (Prevention and Control of Pollution) Amendment Act, 2024, violations were decriminalised into graded monetary penalties of Rs 10,000 to Rs 15 lakh, decided by adjudicating officers with appeal to the National Green Tribunal, and the collections flow into this fund. It is meant to channel penalty money toward environmental protection rather than the general exchequer. Example: A factory penalised under the amended Water Act pays its fine into the Environment Protection Fund after the NGT appeal process.
• Namami Gange: Namami Gange is the Government of India's flagship programme for the rejuvenation of the river Ganga and its tributaries, launched in June 2014 as a Central Sector Scheme with an initial outlay of Rs 20,000 crore up to March 2021. Implemented by the National Mission for Clean Ganga (NMCG), it funds sewage treatment plants, riverfront development, industrial effluent monitoring, afforestation, biodiversity conservation, and public participation. Its pillars include pollution abatement (Nirmal Ganga) and assured ecological flow (Aviral Ganga). Example: It sanctioned sewage treatment capacity of over 5,000 million litres per day along the Ganga and its tributaries.
• Ganga Action Plans: The Ganga Action Plans were the Government of India's early programmes to clean the river Ganga. The first Ganga Action Plan was launched in 1986, targeting sewage interception and treatment in major towns along the river, and a second phase later extended coverage to tributaries and other states. Limited results led to successor frameworks, first the National Ganga River Basin Authority in 2009 and then the Namami Gange mission in 2014. Example: GAP-I (1986) covered 25 Class-I towns in Uttar Pradesh, Bihar and West Bengal, marking India's first major river-cleaning programme.
• Namami Gange Mission-II: Namami Gange Mission-II is the continuation of the Namami Gange programme beyond March 2021, approved with a budgetary outlay of Rs 22,500 crore till 2026. Of this, Rs 11,225 crore covers existing liabilities and Rs 11,275 crore funds new projects and interventions, continuing sewage treatment, riverfront, and biodiversity work. It extends the Ganga river-rejuvenation mission into its second phase under the National Mission for Clean Ganga. Example: Mission-II funds new sewage infrastructure and interventions in the five main-stem Ganga states up to 2026.
• Arth Ganga: Arth Ganga is a development model proposed by the Prime Minister at the first National Ganga Council meeting in Kanpur in December 2019, shifting the emphasis from only cleaning the Ganga (Namami Gange) to linking river rejuvenation with the economic life of the basin. It works through six verticals: zero-budget natural farming, monetisation and reuse of treated water and sludge, livelihood generation, cultural heritage and tourism, people's participation, and institutional capacity building. The idea is that the river's economic value should finance its own conservation. Example: JALAJ livelihood centres, run by trained Ganga Praharis, sell local produce and crafts from the Ganga basin, turning conservation into community income.
• Gangetic dolphin: The Gangetic dolphin (Platanista gangetica) is a freshwater dolphin found in the Ganga-Brahmaputra-Meghna river system, and it was declared India's National Aquatic Animal in 2010. It is listed as Endangered on the IUCN Red List and serves as an indicator species for river health, being threatened by dams, barrages, pollution, sand mining and accidental entanglement in fishing nets. Example: Project Dolphin, announced in 2020, focuses on the conservation of the Gangetic dolphin and other riverine and marine dolphins.
• Ecological flow: Ecological flow (e-flow) is the minimum quantity, timing and quality of water that must continue to flow in a river to sustain its aquatic ecosystems, biodiversity and natural functions such as sediment transport and dilution of pollutants. It requires that dams, diversions and abstractions leave enough water in the river rather than drying stretches of it out. India notified minimum e-flow norms for the Ganga in 2018, making it a legal condition for hydropower and irrigation projects on the river. Example: Hydropower projects on the Ganga must release the notified minimum e-flows even in the lean season to protect aquatic life.
• Marine pollution: The introduction of harmful substances or energy into the marine environment, including plastics, oil, chemicals, nutrients, sewage and noise. About four-fifths of it comes from land-based sources such as rivers, runoff and untreated wastewater, with shipping and offshore activities contributing the rest. It is regulated globally by treaties like MARPOL and the London Protocol. Example: Plastic debris accumulating in ocean gyres and microplastics entering the seafood chain are among the most visible forms of marine pollution today.
• Dead zones: Dead zones are areas of oceans, seas or large lakes where oxygen levels fall so low (hypoxia) that most marine life cannot survive. They are typically caused by nutrient runoff from farms and cities, which fuels algal blooms whose decay consumes dissolved oxygen. It matters for UPSC environment as a flagship example of marine pollution and ecosystem collapse driven by human activity. Example: the Gulf of Mexico dead zone at the mouth of the Mississippi river
• biomagnify: Biomagnification is the process by which the concentration of a persistent pollutant increases at each successive level of a food chain. Non-biodegradable toxins like heavy metals and organochlorine pesticides are absorbed by primary producers and then concentrated in the fatty tissues of herbivores and, most severely, top predators that eat many contaminated prey. The classic consequence is eggshell thinning in birds of prey caused by accumulated DDT. Example: Mercury released into water biomagnifies up the aquatic food chain, reaching dangerous levels in large predatory fish like tuna and shark.
• High Seas Treaty (BBNJ Agreement), 2023: The High Seas Treaty, formally the BBNJ (Biodiversity Beyond National Jurisdiction) Agreement, was adopted on 19 June 2023 under the UN Convention on the Law of the Sea. It is the first legally binding treaty governing the high seas and the deep seabed beyond national jurisdiction, covering benefit-sharing from marine genetic resources, area-based management tools including marine protected areas, environmental impact assessments and capacity building for developing states. It enters into force after 60 ratifications. Example: The treaty creates a legal pathway to establish marine protected areas on the high seas, which were previously impossible under international law.
• Extended Producer Responsibility: Extended Producer Responsibility is the principle that producers, importers and brand owners remain responsible for the environmentally sound management of their products throughout their life cycle, including at end of life. In India it is enforced through EPR rules for plastic packaging, e-waste, batteries and tyres, with targets, tradable EPR certificates and environmental compensation for non-compliance. It shifts the cost of waste management from municipalities to those who place the products in the market. Example: Under plastic waste EPR, producers of plastic packaging must ensure a mandated share of it is collected and recycled each year.
• Oil pollution: Contamination of water, and sometimes soil, by petroleum or petroleum products from spills, tanker accidents, offshore drilling, pipeline leaks and routine discharges such as bilge water. Oil coats marine life and smothers sensitive habitats like mangroves and coral reefs, and it is difficult to remove because it spreads as a thin film over large areas. Even small, repeated discharges accumulate into serious ecological harm. Example: The 1989 Exxon Valdez spill in Alaska released about 11 million gallons of crude oil, devastating coastal wildlife and shorelines for years.
• Water trading: Water trading is a market based mechanism that treats water, or treated wastewater, as a tradable commodity so that it moves from lower value to higher value uses through buying and selling of water rights or entitlements. It can improve allocation efficiency in water scarce regions, but it raises equity concerns about pricing out small farmers and the poor from a basic necessity. In India the operative instrument being developed on these lines is the tradable Water Reuse Certificate for treated wastewater. Example: Australia's Murray Darling Basin runs one of the world's most developed water markets, where farmers buy and sell seasonal water allocations.
• MWRRA: The Maharashtra Water Resources Regulatory Authority, a statutory body set up under the Maharashtra Water Resources Regulatory Authority Act, 2005, to regulate water allocation, set bulk water tariffs and ensure equitable distribution across sectors in the state. In Maharashtra's water governance, it has pushed measures such as mandating 20 per cent effluent reuse, a framework endorsed by NITI Aayog. Example: The authority's effluent-reuse mandate illustrates how state water regulators can drive treated-wastewater recycling in water-stressed regions.
• AMRUT 2.0: The second phase of the Atal Mission for Rejuvenation and Urban Transformation, launched in October 2021 with an outlay of Rs 2.77 lakh crore, aimed at making Indian cities water-secure. It targets universal tap-water coverage in all statutory towns and sewerage or septage management in 500 AMRUT cities. Example: it builds on AMRUT (2015), which focused on basic urban infrastructure in 500 cities. Example: Rs 2.77 lakh crore mission (launched October 2021) for universal tap water and sewerage in 500 cities.
• Swachh Bharat Mission 2.0: Swachh Bharat Mission 2.0 is the second phase of the urban cleanliness mission, launched on 1 October 2021. It aims to make all statutory towns garbage-free by achieving 100 percent source segregation, door-to-door collection, scientific processing of municipal solid waste, remediation of legacy dumpsites, and ODF+ and ODF++ certification for sanitation. Example: Indore's model of 100 percent waste segregation and processing is showcased under Swachh Bharat Mission 2.0.
• Atal Bhujal Yojana: Atal Bhujal Yojana (ATAL JAL) is a Central Sector Scheme for community-led groundwater management in water-stressed areas, launched to mark former Prime Minister Atal Bihari Vajpayee's birth anniversary and implemented from 2020-21 for five years. With a Rs 6,000 crore outlay, half financed by a World Bank loan, it marks a shift from supply-side augmentation to demand-side management through panchayat-led water security plans, water budgeting, and behavioural change. It covers about 8,350 gram panchayats across 7 states. Example: The seven participating states are Gujarat, Haryana, Karnataka, Madhya Pradesh, Maharashtra, Rajasthan, and Uttar Pradesh.
• Jal Shakti Abhiyan: Catch the Rain: A nationwide water-conservation campaign launched by the Prime Minister on 22 March 2021, World Water Day, with the theme Catch the rain, where it falls, when it falls, implemented by the Ministry of Jal Shakti. Covering all districts in rural and urban areas, it promotes rainwater harvesting structures, revival of traditional water bodies, enumeration and geo-tagging of water bodies, setting up of Jal Shakti Kendras and intensive afforestation through people's participation. Example: The campaign nudges states, panchayats and citizens to build rooftop rainwater harvesting and recharge structures suited to local rainfall and soil conditions before each monsoon.
• Mission Amrit Sarovar: Mission Amrit Sarovar, launched on 24 April 2022 by the Ministry of Rural Development, aimed to construct or rejuvenate 75 water bodies (Amrit Sarovars) in every district of India, totalling about 50,000, as part of Azadi ka Amrit Mahotsav. Each sarovar was to have a pondage area of about one acre and a water-holding capacity of about 10,000 cubic metres, built by converging schemes such as MGNREGS and 15th Finance Commission grants. The mission targets water conservation and groundwater recharge with community participation. Example: More than 68,000 Amrit Sarovars had been completed by early 2025, exceeding the original 50,000 target.
• PMKSY-Per Drop More Crop: The micro-irrigation component of PMKSY, administered by the Department of Agriculture and Farmers Welfare, which subsidises drip and sprinkler systems for farmers. It promotes water-use efficiency in agriculture by delivering water directly to plant roots, with higher subsidy rates for small and marginal farmers. It is central to the goal of getting more crop per drop of water. Example: Sugarcane farmers in Maharashtra have adopted drip irrigation under Per Drop More Crop, cutting water use per quintal of cane significantly.
• National Water Mission: The National Water Mission is one of the eight missions under the National Action Plan on Climate Change, launched in 2011. Its objective is the integrated management of water resources and a 20 percent improvement in water use efficiency through pricing, better technologies and basin-level planning. It promotes wastewater recycling, water-neutral industries and the participation of states in groundwater management. Example: The mission supports the adoption of micro-irrigation and wastewater reuse in water-stressed regions.
• river interlinking: River interlinking is the large-scale transfer of water from surplus river basins to deficit basins through canals, reservoirs and pumping stations, aiming to reduce floods and droughts at the same time. In India it follows the National Perspective Plan of 1980, prepared by the National Water Development Agency, which identified 30 such links. Supporters see it as a solution to water scarcity, while critics warn of ecological damage, displacement and high costs. Example: The Ken-Betwa Link, approved by the Union Cabinet in December 2021, will transfer Ken river water to the Betwa basin to irrigate drought-prone Bundelkhand.
• Ken-Betwa link: The Ken-Betwa link is India's first river interlinking project under the National Perspective Plan, transferring surplus Ken water to the Betwa basin in Madhya Pradesh and Uttar Pradesh for drought-prone Bundelkhand. With the Daudhan Dam, a 216 km canal and allied works costing Rs 44,605 crore, it promises 10.62 lakh hectares of irrigation, drinking water for 62 lakh people and 103 MW of hydropower by 2030. It matters for GS-1 geography and GS-3 water management, plus Panna Tiger Reserve debate. Example: Foundation stone laid by the Prime Minister on 25 December 2024
• Article 21: Article 21 guarantees that no person shall be deprived of life or personal liberty except according to procedure established by law. Through judicial interpretation, beginning with Maneka Gandhi (1978), it has expanded to cover dignity, privacy, and a clean environment. It is the most litigated Fundamental Right and central to GS-2 polity. Example: the Supreme Court reading privacy into Article 21 in Justice K.S. Puttaswamy v. Union of India (2017).
• Key takeaways: Key takeaways is a quick-revision summary box placed at the end of each article, listing the most exam-relevant points in a short numbered list. It distils definitions, dates, figures, provisions and examples into a form suited for last-minute revision before Prelims and Mains. Together with the article's practice questions, it turns every topic into a self-contained study unit.
• Biochemical Oxygen Demand (BOD): Biochemical Oxygen Demand is the amount of dissolved oxygen required by microorganisms to break down organic matter in a water sample over a specified period, usually five days at 20 degrees Celsius (BOD5). It is a key indicator of organic pollution: the higher the BOD, the more polluted the water, because decomposing organic waste consumes the oxygen that aquatic life needs. BOD is a standard parameter in water quality monitoring and effluent discharge norms under India's environmental regulations. Example: Clean river water typically has a BOD below 5 mg per litre, while untreated sewage can exceed 200 mg per litre.
• Dissolved oxygen (DO): Dissolved oxygen (DO) is the amount of free oxygen dissolved in water, measured in milligrams per litre, and it is a primary indicator of water quality. Fish and other aquatic life need adequate DO to breathe; levels below about 4 mg/L stress most species, and near-zero levels create dead zones where little can survive. Organic pollution depletes DO because decomposer microbes consume oxygen while breaking down the waste, a relationship captured by the Biochemical Oxygen Demand (BOD) test. Example: Mass fish kills in urban lakes are typically traced to sewage inflows that crash dissolved oxygen to near zero.
• Central Pollution Control Board (CPCB): The Central Pollution Control Board (CPCB) is India's apex pollution watchdog, constituted in September 1974 under the Water (Prevention and Control of Pollution) Act, 1974, with additional functions under the Air (Prevention and Control of Pollution) Act, 1981. It advises the central government, lays down national standards for air and water quality and effluent discharge, and coordinates the work of State Pollution Control Boards. It also monitors implementation of waste management rules for plastic, e-waste, biomedical and hazardous waste. Example: CPCB's colour-coded categorisation of industries into red, orange, green and white categories guides consent requirements under pollution laws.
• State Pollution Control Boards (SPCBs): State Pollution Control Boards are statutory bodies constituted under the Water (Prevention and Control of Pollution) Act 1974, with functions extended under the Air Act 1981. They advise the state government on pollution matters, lay down effluent and emission standards, grant or refuse Consent to Establish and Consent to Operate to industries, and monitor compliance with environmental laws. Example: An SPCB grants Consent to Operate to a factory only after its effluent treatment plant meets the prescribed discharge standards.
• National Green Tribunal: The National Green Tribunal is a statutory environmental court established on 18 October 2010 under the National Green Tribunal Act, 2010, with its principal bench in New Delhi and circuit benches across India. It adjudicates cases on environmental protection, applies the polluter pays and precautionary principles, is not bound by the Civil Procedure Code, and is guided by natural justice. It matters for UPSC as GS-2/GS-3 environment governance, frequently cited in mains answers on environmental justice. Example: The NGT ordered the closure of the Sterlite copper plant at Thoothukudi, Tamil Nadu, in 2018 over pollution concerns
• National Mission for Clean Ganga (NMCG): The National Mission for Clean Ganga is a registered society set up in 2011 under the Ministry of Jal Shakti that implements the Namami Gange programme for cleaning and conserving the Ganga. It coordinates pollution abatement projects such as sewage treatment plants, riverfront development, afforestation along the river and community engagement through Ganga Praharis. The mission also supports the National Ganga Council chaired by the Prime Minister for overall direction. Example: NMCG funded sewage treatment projects in cities like Kanpur and Varanasi to stop untreated waste flowing into the Ganga.
• MARPOL (1973/78): The International Convention for the Prevention of Pollution from Ships, adopted by the International Maritime Organization in 1973 and modified by a 1978 Protocol. It regulates vessel-source marine pollution through six annexes covering oil, noxious liquid substances, harmful packaged substances, sewage, garbage and air emissions. It is the principal global treaty controlling operational and accidental pollution from ships. Example: MARPOL Annex VI caps the sulphur content of ships' fuel oil, which forced the global shipping industry to switch to cleaner fuels from 2020.
• Water Reuse Certificate (WRC): The Water Reuse Certificate is a proposed tradable permit instrument in India that treats treated wastewater as a marketable commodity, on the model of carbon credits. Entities that treat and reuse wastewater earn certificates which deficit users or regulated industries can buy to meet reuse obligations, so water flows to its most productive use. It was developed with the World Bank hosted 2030 Water Resources Group as a market based answer to India's very low wastewater reuse rate. Example: An industry that recycles its effluent beyond the mandated level could sell its surplus Water Reuse Certificates to another unit struggling to meet its reuse target.
• 2030 Water Resources Group: The 2030 Water Resources Group (2030 WRG) is a public-private-civil society partnership working to close the gap between water demand and supply, incubated at the World Economic Forum, managed by the IFC from 2012 and hosted by the World Bank's Water Global Practice since 2018. It provides a neutral platform where governments, companies and civil society jointly design water security and climate adaptation programmes in 11 countries including India. Example: In Uttar Pradesh, the 2030 WRG's PRAGATI Accelerator helps small and marginal farmers adopt water-efficient and climate-smart agricultural practices.
• Central Ground Water Authority: The Central Ground Water Authority (CGWA) is India's national regulator for groundwater development and management, constituted in January 1997 under Section 3(3) of the Environment (Protection) Act, 1986, following a Supreme Court directive in the M.C. Mehta case. Functioning under the Ministry of Jal Shakti, it issues No Objection Certificates for groundwater extraction, notifies over-exploited and critical areas, and classifies assessment units as safe, semi-critical, critical or over-exploited. Example: An industry seeking to pump groundwater for manufacturing must obtain an NOC from CGWA, which is mandatory in notified critical and over-exploited blocks.
• Subhash Kumar v. State of Bihar (1991): In Subhash Kumar v. State of Bihar (1991), the Supreme Court held that the right to life under Article 21 includes the right to pollution-free water and air. It ruled that citizens can approach the courts through writ petitions to seek enforcement of this right, anchoring environmental protection as an enforceable fundamental right. Example: The judgment is cited to establish that environmental rights are part of Article 21 and enforceable through writ jurisdiction.
• A.P. Pollution Control Board v. M.V. Nayudu (2000): A Supreme Court judgment holding that the precautionary principle and the polluter pays principle are part of the law of the land and of sustainable development under Article 21 of the Constitution. It ruled that where there are threats of serious or irreversible environmental damage, lack of full scientific certainty cannot be used as a reason for postponing cost-effective preventive measures. Example: it is the leading Indian authority cited when courts or regulators invoke the precautionary principle to restrict a potentially polluting activity pending fuller scientific evidence. Example: The leading authority for applying the precautionary principle and polluter pays principle in Indian environmental law.

• Fly ash: Fly ash is the fine residue left when coal is burnt in thermal power plants, captured from flue gases, and it is India's largest industrial solid waste stream by volume. Unmanaged, it leaches heavy metals and blows into habitations; utilised, it becomes raw material. Example: Fly ash bricks and Portland pozzolana cement turn power-plant waste into construction material.

• 100 per cent fly ash utilisation (2021 notification): The 2021 fly ash utilisation notification set a phased roadmap toward 100 per cent utilisation of ash generated by thermal power plants, with penalties for non-compliance and defined end-uses such as bricks, cement, embankments and mine filling. Example: A plant that once dumped ash in ponds must now show utilisation against the notified targets.

• Integrated Water Resources Management: Integrated Water Resources Management (IWRM) is the coordinated planning of surface water, groundwater and land as one system, guided by the Dublin Principles of 1992. Example: merging river and aquifer planning instead of letting separate boards license the same water twice.
• Hypoxia: Hypoxia is the state of very low dissolved oxygen in water, produced when nutrient-fed algal blooms decompose and consume oxygen, creating a dead zone. Example: seasonally oxygen-starved patches mapped in the northern Indian Ocean.
• Ocean acidification: Ocean acidification is the fall in ocean pH caused by absorption of human carbon dioxide emissions, with surface acidity up about 30 percent since the industrial era. Example: slower coral skeleton growth and failing shellfish larvae in acidifying waters.

Prelims practice