Sustainability & Environment (Agri-Food Systems) · Natural Resources & Biodiversity · also Water Resource Conservation, Water Management for Sustainability, Integrated Water Resources Management
Using less water to grow food and sharing it fairly: water productivity, water footprint accounting, groundwater depletion, rainwater harvesting and the institutions that govern water. Irrigation system design is in the Agricultural Engineering track; water pricing economics is in the Agribusiness track.
In the exams: ICAR AIEEA-PG Water Science & Technology group; GATE ES Section 4 (water conservation, rainwater harvesting); ICAR AICE subject 71 Unit 1
Agriculture is the world's largest user of fresh water. Irrigation accounts for about 70% of global freshwater withdrawals, and much more in many dry countries; irrigated land, though only about a fifth of cropland, produces around 40% of the world's food. As populations, diets and incomes grow and climate change alters rainfall, competition for water among farms, cities, industry, energy and ecosystems is intensifying. Aquifers in north-west India, the North China Plain, the High Plains of the United States and the Middle East are being depleted; rivers such as the Colorado, Yellow, Indus and Murray-Darling no longer reach the sea in some years; and conflicts over shared rivers recur.
This subject is about using less water to grow food and sharing it fairly. It covers how water scarcity is measured and how water links to food and energy; water productivity and the catchphrase 'more crop per drop', including the paradox that efficiency can increase consumption; water footprints and virtual water trade; groundwater depletion and aquifer management; rainwater harvesting and managed aquifer recharge; reuse of wastewater in agriculture; and the institutions that govern water -- integrated water resources management, water rights and allocation, participatory irrigation management, river basin and transboundary governance, and the water stewardship standards now used by agri-food companies.
Neighbouring subjects are referred to rather than repeated. Irrigation system design, pumps and drainage engineering are in the Agricultural Engineering track; water pricing and the economics of water as an economic good are in the Agribusiness track (Natural Resource and Environmental Economics); water quality and diffuse pollution are in Water Quality and Agricultural Non-point Source Pollution; and the hydrological cycle and groundwater hydraulics basics are in Hydrology and Water Resources.
The subject is examined in ICAR AIEEA-PG (Water Science and Technology), GATE Environmental Science and Engineering (Section 4, water conservation and rainwater harvesting), the ICAR PhD paper in Environmental Sciences (Unit 1, watershed and natural resources), UGC NET and UPSC (groundwater, interstate and transboundary rivers, Jal Shakti programmes), and in professional roles in water ministries, river basin organisations, irrigation agencies, development banks and corporate water stewardship. Figures quoted are commonly cited global estimates and vary by source and year.
Several indicators measure water scarcity, each capturing a different aspect. The Falkenmark indicator divides a country's renewable freshwater resources by its population: below about 1,700 cubic metres per person per year indicates water stress, below 1,000 scarcity and below 500 absolute scarcity. It is simple but ignores how much water is actually used, differences within countries and the ability to adapt. The withdrawal-to-availability ratio (criticality ratio) compares annual withdrawals with renewable resources; above about 40% is considered high stress. Sustainable Development Goal indicator 6.4.2 ('level of water stress') measures freshwater withdrawal as a percentage of available freshwater resources after allowing for environmental flow requirements, and indicator 6.4.1 tracks water-use efficiency as economic value added per cubic metre withdrawn.
The International Water Management Institute's Comprehensive Assessment of Water Management in Agriculture (2007) distinguished physical water scarcity -- where use approaches or exceeds sustainable limits, as in the Middle East, North Africa, north-west India and northern China -- from economic water scarcity, where water is available but lack of investment, institutions or human capacity prevents access, as in much of sub-Saharan Africa. Scarcity also varies seasonally and between years; monthly blue-water scarcity analyses show that many river basins face severe scarcity for part of each year even if annual averages look comfortable.
Water, food and energy are interdependent. Agriculture uses most withdrawals and is affected by energy prices (pumping, fertiliser). Energy production uses water for cooling thermal power plants, hydropower, biofuel crops and fuel extraction. Water supply uses energy for pumping, treatment, desalination and transport. Decisions in one sector therefore affect the others: subsidised electricity for farm pumping in parts of India has encouraged groundwater depletion and burdened electricity utilities; expanding biofuels can raise irrigation demand; building dams for hydropower changes water available downstream for irrigation and fisheries. The nexus approach, promoted after a 2011 conference in Bonn, argues for planning these sectors together to find synergies (such as solar pumping with controlled extraction, or reuse of treated wastewater for irrigation) and to avoid one sector's gains causing another's losses. Climate change adds stress through changing rainfall, higher evaporation and more frequent droughts and floods. Nexus thinking is most useful at the level of concrete decisions -- for example, whether to pair a subsidy for solar irrigation pumps with metering and a feed-in tariff that pays farmers to sell surplus power rather than pump more water, or whether a new hydropower dam should be operated to release water for downstream irrigation in the dry season.
Water productivity (WP) is output per unit of water. Crop water productivity is usually defined as yield divided by evapotranspiration (kilograms per cubic metre of water consumed), and irrigation water productivity as yield (or yield increment) per cubic metre of irrigation water applied or withdrawn. Economic water productivity uses value instead of mass. Because 1 mm of water over 1 hectare is 10 cubic metres, a crop yielding 5,000 kg/ha with evapotranspiration of 500 mm (5,000 m3/ha) has a crop water productivity of 1.0 kg/m3. Values differ widely: cereals typically range from well under 1 to around 2 kg/m3, with large gaps between farmers in the same region, which indicates room for improvement through better agronomy as much as through irrigation technology.
The yield response to water is described by the FAO relationship (Doorenbos and Kassam, FAO Irrigation and Drainage Paper 33): (1 - Ya/Ym) = Ky (1 - ETa/ETm), where Ya and Ym are actual and maximum yield, ETa and ETm actual and maximum evapotranspiration, and Ky the yield response factor; crops and growth stages with Ky above 1 are especially sensitive to water deficit. FAO's AquaCrop model (Paper 66) builds on this to simulate yield under water limitation and guide deficit irrigation, in which crops are deliberately under-irrigated during less sensitive stages to save water with small yield losses.
Raising water productivity is the core of 'more crop per drop', a slogan used by FAO and in India's Pradhan Mantri Krishi Sinchayee Yojana ('Per Drop More Crop' component, from 2015), which subsidises drip and sprinkler systems. Options include better crop management (varieties, fertility, weed control, timely sowing), reducing non-beneficial evaporation (mulching, drip, reduced bare soil), deficit irrigation, alternate wetting and drying and direct-seeded rice, laser land levelling, and better scheduling based on soil moisture or crop evapotranspiration.
But irrigation efficiency must be judged at basin scale. Classical efficiency (water beneficially used by crops divided by water applied) treats seepage and runoff as losses, yet much of this 'lost' water returns to rivers and aquifers and is reused downstream. A more accurate accounting separates the consumed fraction (evapotranspiration, which leaves the basin's usable supply) from the non-consumed fraction (return flows, recoverable or not). Switching from flood to drip irrigation reduces applied water, but if farmers use the saved water to expand irrigated area or grow thirstier crops, total evapotranspiration -- consumption -- can rise, reducing return flows to others and to aquifers. This 'irrigation efficiency paradox', documented in many basins, means efficiency subsidies save real water only when combined with caps on consumption or allocations. Water savings are real when non-beneficial evaporation or flows to sinks (saline groundwater, the sea) are reduced.
The water footprint, developed by Arjen Hoekstra and colleagues and standardised in the Water Footprint Assessment Manual (2011), measures the volume of fresh water used to produce a product, by a person, a business or a nation, along the full supply chain. It has three components. The green water footprint is rainwater stored in the soil and evapotranspired by crops and pasture. The blue water footprint is surface water or groundwater consumed -- evaporated, incorporated into products or transferred to another catchment -- not simply withdrawn. The grey water footprint is the volume of fresh water needed to assimilate pollutants to meet ambient water quality standards, calculated as the pollutant load divided by the difference between the maximum acceptable concentration and the natural background concentration.
For crops, the green and blue footprints per tonne are evapotranspiration (green or blue) divided by yield, using 1 mm = 10 m3/ha. Global averages show large differences between products -- beef and nuts have high footprints per kilogram, cereals moderate, vegetables low -- but within-product variation between places is also large, and the share of blue water matters more for scarcity than the total volume.
The volumetric water footprint has been criticised for adding litres of very different significance: a litre of rainwater on pasture in a wet region has little opportunity cost, while a litre of groundwater pumped from a depleting aquifer in a dry region has a high one. Life-cycle assessment approaches therefore weight water consumption by local scarcity. ISO 14046:2014 sets principles for water footprint assessment within LCA, and the AWARE method (from the WULCA working group of the UNEP-SETAC Life Cycle Initiative) provides characterisation factors representing the relative available water remaining per area in a watershed after human and ecosystem demands. A Water Footprint Network-style assessment includes a sustainability assessment that compares blue footprints with blue water availability in each basin and month.
For agri-food companies, water footprints identify hotspots -- often irrigated ingredients sourced from water-stressed basins -- and guide sourcing, supplier engagement and stewardship (chapter 11). For consumers and policymakers, they illustrate the hidden water in diets and trade, but should not be used alone to rank products without considering scarcity, water quality and other impacts.
A wheat crop yields 4 t/ha and evapotranspires 450 mm over the season, of which 300 mm comes from rainfall stored in the soil and 150 mm from irrigation. The green water footprint is 300 mm x 10 = 3,000 m3/ha, divided by 4 t = 750 m3 per tonne; the blue footprint is 1,500 m3/ha / 4 t = 375 m3 per tonne. If 20 kg N/ha leaches and the ambient standard is 11.3 mg/L nitrate-N against a natural background of 1 mg/L, the grey footprint is 20 kg / (0.0113 - 0.0010) kg/m3 = about 1,940 m3/ha, or about 485 m3 per tonne. The total is roughly 1,610 m3 per tonne. The numbers show that the grey component can be as large as the blue one, that irrigation is a modest share of total water in this case, and that reducing nitrate leaching shrinks the footprint as effectively as saving irrigation water. They also show the method's sensitivity to choices such as the standard used for the grey component.
Virtual water, a term introduced by Tony Allan in the early 1990s, is the water embedded in the production of goods, especially food. When a country imports a tonne of wheat, it effectively imports the water used to grow it. Allan argued that water-scarce countries in the Middle East and North Africa had avoided water wars partly by importing grain, which allowed them to support populations far beyond what their own water could feed. Global trade in agricultural products moves large volumes of virtual water each year, a substantial fraction of all water used in agriculture.
In principle, trade can save water globally when products move from places where they are produced with little water (high water productivity, abundant green water) to places where they would need much irrigation. Analyses suggest global cereal trade has saved water in this sense. Some exporters, however, export virtual water from stressed resources: India's exports of rice and other crops grown with depleting groundwater in Punjab and Haryana, Pakistan's exports from the Indus basin, and exports of irrigated fruit, nuts and fodder from water-stressed regions of the United States, Spain and the Middle East are examples.
Virtual water is a useful lens but a weak policy rule. Trade patterns are driven by land, labour, capital, technology, policy and markets, not by water alone; water is usually a small share of production costs. Comparative advantage depends on the opportunity cost of water in each place, which volumetric figures do not show. Importing food reduces local water demand but increases dependence on world markets and exposure to price shocks, a real concern for food security. Green and blue virtual water have very different implications: exporting rain-fed wheat from a wet region costs little, while exporting crops irrigated from a depleting aquifer imposes a real long-term cost. Finally, water policy that ignores farmers' livelihoods in exporting regions is unlikely to succeed.
For India, the debate centres on whether procurement and power subsidies that encourage rice in the north-west -- effectively exporting groundwater through rice to other states and abroad -- should be reformed to favour crop diversification towards less water-intensive crops, and on how to protect farm incomes during such a transition.
Groundwater supplies a large share of irrigation water worldwide and most drinking water in many countries. India is the world's largest user of groundwater, extracting roughly a quarter of the global total, mostly for irrigation through millions of private wells and tube wells. Depletion occurs when abstraction exceeds recharge over the long term, lowering water tables, drying shallow wells, increasing pumping costs, causing land subsidence (as in parts of California's Central Valley, Mexico City and Jakarta), seawater intrusion in coastal aquifers, and reduced baseflow to rivers and wetlands. Satellite gravimetry from the GRACE missions has revealed major depletion hotspots, including north-west India (Punjab, Haryana, Rajasthan and Delhi), the North China Plain, the US High Plains (Ogallala) aquifer, California's Central Valley and the Middle East. Groundwater quality problems -- geogenic arsenic in the Bengal basin, fluoride in parts of India and East Africa, salinity and nitrate -- further limit usable supply.
In India, the Central Ground Water Board assesses each block by the stage of groundwater extraction, the ratio of annual extraction to annual extractable resource: up to 70% is 'safe', 70-90% 'semi-critical', 90-100% 'critical' and above 100% 'over-exploited'. Many blocks in Punjab, Haryana, Rajasthan and parts of south India fall in the over-exploited category.
Groundwater is a classic common-pool resource: many users draw from a shared stock, and each benefits from pumping while sharing the cost of depletion. Management tools include monitoring and data (water levels, abstraction metering), well registration and permits, abstraction limits and pumping quotas, restrictions on new wells in over-exploited areas, energy policy (separating agricultural electricity feeders and rationing hours, as Gujarat did under the Jyotigram scheme from 2003; replacing flat-rate power with metered supply), crop policy (shifting away from water-intensive crops, adjusting sowing dates -- Punjab's Preservation of Subsoil Water Act 2009 delays paddy transplanting until mid-June to reduce pumping in the hottest weeks), managed aquifer recharge (chapter 6), and community-based groundwater management. India's Atal Bhujal Yojana (from 2020) supports community-led groundwater management in water-stressed blocks of several states, and model groundwater bills have proposed public-trust approaches.
In India groundwater rights have traditionally been attached to land ownership (reflecting the Indian Easements Act 1882), which makes regulation of private pumping difficult. Elsewhere, the United States and Australia use permits and adjudicated rights, and some basins (such as under California's Sustainable Groundwater Management Act 2014) require local agencies to bring basins into balance. Effective groundwater governance combines data, rules, enforcement, incentives and community participation; technology alone, such as subsidised micro-irrigation, does not halt depletion if total extraction is not limited.
The volume of groundwater lost can be estimated from the fall in the water table, the area and the aquifer's specific yield (the fraction of aquifer volume that drains under gravity). A district of 1,000 square kilometres (100,000 hectares) where the water table falls by 1 metre a year in an unconfined aquifer with specific yield 0.12 loses about 1,000,000,000 m2 x 1 m x 0.12 = 120 million cubic metres, or 0.12 cubic kilometres, of stored water each year. Spread over 100,000 ha of irrigated land, that is about 1,200 m3 per hectare, or 120 mm of water depth, drawn from storage beyond what recharge replaces. Comparing this with typical rice irrigation of 1,000-2,000 mm a season shows why changing crops and sowing dates, rather than small efficiency gains, is often needed to stabilise such aquifers. The same reasoning lies behind the 'water table fluctuation' method of estimating recharge, using the seasonal rise after the monsoon.
Rainwater harvesting collects and stores runoff for use or recharge. At household scale, rooftop systems feed tanks or recharge pits; harvestable volume = catchment area x rainfall x runoff coefficient (the fraction of rain that becomes runoff, high for hard roofs and low for vegetated land). At farm and village scale, farm ponds, check dams across streams, percolation tanks, contour bunds and trenches capture runoff for supplementary irrigation or recharge. Traditional systems are rich and varied: the tanks of south India, johads and kunds in Rajasthan, ahar-pyne systems in Bihar, zing in Ladakh, and qanats and falaj elsewhere. Community revival of johads by voluntary organisations in Alwar district, Rajasthan, has been credited with restoring the flow of small rivers.
India's watershed development programmes and the Jal Shakti Abhiyan campaign ('Catch the Rain') promote harvesting at scale. Rainwater harvesting can buffer dry spells, raise local water tables and improve drinking-water security. But at basin scale it redistributes rather than creates water: runoff captured upstream is no longer available to downstream users and reservoirs, so intensive harvesting in a closed basin can reduce inflows to downstream tanks and rivers. Planning must therefore consider the whole basin's water balance, especially where downstream users or ecosystems depend on runoff.
A school roof of 100 m2 in a place receiving 800 mm of rain a year, with a runoff coefficient of 0.8 for a hard roof, can harvest about 100 x 0.8 x 0.8 = 64 m3 a year -- enough to supply drinking water for many pupils if stored and treated, or to recharge a well. A farm pond fed by a 2 ha catchment of cropland receiving 600 mm of rain, with a runoff coefficient of 0.2, can capture about 20,000 m2 x 0.6 m x 0.2 = 2,400 m3, minus evaporation and seepage; that might provide one or two protective irrigations to a hectare of crop during a dry spell. The calculations show both the value of harvesting for buffering short droughts and its limits: harvested volumes are small compared with full irrigation demands, and capturing them reduces runoff available to others.
Managed aquifer recharge (MAR) intentionally adds water to aquifers for later recovery or environmental benefit. Methods include spreading methods (infiltration basins, flooding of fields in the wet season, recharge trenches), in-channel structures (check dams, sand dams, percolation tanks that hold water so it infiltrates), well methods (injection wells, aquifer storage and recovery wells that inject water when it is plentiful and pump it out when needed), riverbank filtration, and soil-aquifer treatment of treated wastewater, which uses passage through soil to further purify it. Sources of water include monsoon runoff, floodwater, surplus canal water, and treated wastewater.
MAR can store water underground with little evaporation, restore depleted aquifers, counter seawater intrusion and improve water quality, but it requires suitable geology (permeable soils and aquifer storage), water of adequate quality to avoid clogging and contamination, monitoring to verify recharge, and rules that ensure recharged water is not simply pumped out by the nearest users. Its effects are often overestimated when recharge is assumed rather than measured. Successful schemes, such as large infiltration programmes in arid regions and aquifer storage and recovery for cities, combine engineering with governance of extraction.
Treated and untreated wastewater is used to irrigate crops on a large scale, especially around cities in water-scarce regions. Reuse provides a reliable supply that grows with urban population and is available in droughts, supplies nutrients (nitrogen and phosphorus) that reduce fertiliser needs, reduces discharge of effluent to rivers, and frees fresh water for other uses. Israel reuses most of its treated municipal wastewater for agriculture, and Spain, Jordan, Tunisia, California and Australia have substantial reuse. In many low- and middle-income countries, much reuse is informal and unplanned: farmers irrigate vegetables with untreated or partly treated wastewater from urban drains and rivers, which supports livelihoods and urban food supply but creates health risks.
Sodicity and salinity are agronomic concerns for both wastewater and other marginal waters. The sodium adsorption ratio, SAR = Na / sqrt[(Ca + Mg) / 2] with concentrations in milliequivalents per litre, indicates the risk that sodium will disperse soil and reduce infiltration; electrical conductivity indicates salinity. High SAR and high salinity require soil management such as gypsum application and leaching.
Health risks come from pathogens (bacteria, viruses, protozoa and helminth eggs) that can infect farm workers and consumers, especially of vegetables eaten raw. Chemical risks include heavy metals from industrial discharges, salts and boron, and contaminants of emerging concern -- pharmaceuticals, antibiotic residues and resistance genes, PFAS and microplastics -- whose long-term effects are uncertain. The WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater (2006) take a risk-based, multiple-barrier approach: a health-based target (a tolerable additional disease burden, expressed in disability-adjusted life years) is met by combining partial treatment with crop restrictions, irrigation methods (drip reduces contact), withholding periods before harvest, washing and cooking of produce, and protective measures for workers. This allows safe use where full treatment is unaffordable. Sanitation Safety Planning applies the approach locally.
The European Union's Regulation (EU) 2020/741 on minimum requirements for water reuse, applicable since 2023, defines classes of reclaimed water quality (from class A, for food crops eaten raw where the edible part contacts the water, to class D, for industrial, energy and seeded crops) with limits for E. coli, BOD, suspended solids and turbidity, and requires risk management plans. India's guidelines encourage treated wastewater reuse in agriculture and industry, and several states have reuse policies. Public acceptance, reliable treatment performance, monitoring and clear allocation of reclaimed water are key to successful schemes.
Integrated Water Resources Management (IWRM) emerged as the dominant paradigm of water governance in the 1990s. The Dublin Statement of the International Conference on Water and the Environment (1992) set out four principles: fresh water is a finite and vulnerable resource, essential to sustain life, development and the environment; water development and management should be based on a participatory approach involving users, planners and policymakers at all levels; women play a central part in the provision, management and safeguarding of water; and water has an economic value in all its competing uses and should be recognised as an economic good. The Global Water Partnership defined IWRM (2000) as a process that promotes the coordinated development and management of water, land and related resources in order to maximise the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems.
IWRM emphasises managing water at the scale of river basins and aquifers rather than administrative units; coordinating across sectors (agriculture, urban supply, energy, environment); linking land use and water; managing surface and groundwater together; balancing supply-side development with demand management; and involving stakeholders. Sustainable Development Goal target 6.5 calls for implementing IWRM at all levels by 2030, tracked by indicator 6.5.1 (degree of IWRM implementation) and 6.5.2 (transboundary cooperation).
Many countries have adopted IWRM in water laws and policies: the EU Water Framework Directive organises management by river basin districts; South Africa's National Water Act (1998) created catchment management agencies and a reserve for basic human needs and ecosystems; Brazil's 1997 water law established basin committees and charges for water use; India's National Water Policy (2012) adopted many IWRM elements, recognising water as a common pool resource held by the state in public trust and calling for basin-level planning.
Critics argue that IWRM is too vague to guide action, that it has often become a donor-driven checklist, that 'integration' is difficult across powerful sectoral ministries, and that treating water as an economic good can conflict with the human right to water (recognised by the UN General Assembly in 2010). Practitioners now favour pragmatic, problem-focused approaches -- adaptive management, nexus thinking, water security -- that keep IWRM's core ideas while concentrating on specific outcomes such as reducing groundwater depletion or securing environmental flows.
Water rights define who may use water, how much, when and under what conditions. The riparian doctrine, rooted in English common law and used in wetter regions such as the eastern United States, gives landowners adjoining a water body the right to reasonable use. Prior appropriation ('first in time, first in right'), developed in the arid western United States, gives priority to whoever first put water to beneficial use, regardless of land ownership; in shortages, junior rights are cut first. The public trust doctrine holds that certain waters are held by the state for the public; the 1983 Mono Lake decision in California used it to protect a lake's ecosystem against diversions. Customary and religious water rights remain important in many countries.
Allocation mechanisms include administrative allocation by government agencies, user-based allocation through associations and communities, and market-based allocation where rights are tradable. Australia's water reforms unbundled water entitlements from land, introduced caps on diversions and created active water markets in the Murray-Darling Basin, with the Basin Plan (2012) recovering water for the environment; Chile's 1981 Water Code created private, tradable rights with limited state oversight, criticised for concentration and environmental harm and reformed in 2022. In India, surface water is generally regarded as state property allocated administratively, while groundwater has been tied to land ownership. Environmental flows -- the quantity, timing and quality of flow needed to sustain freshwater ecosystems -- are increasingly treated as a legitimate allocation, as in South Africa's ecological reserve and the Brisbane Declaration (2007, updated 2018).
Many large public irrigation systems in Asia, Africa and Latin America have suffered from poor maintenance, low fee collection, inequitable distribution between head-end and tail-end farmers, and low productivity. Participatory irrigation management (PIM) and irrigation management transfer (IMT) shift responsibility for operating and maintaining parts of systems, collecting fees and distributing water to water user associations (WUAs) of farmers. Mexico transferred most of its irrigation districts to user organisations in the 1990s; in India, Andhra Pradesh's Farmers' Management of Irrigation Systems Act (1997) was the first large-scale state law creating elected WUAs, followed by other states such as Maharashtra (2005).
Evidence is mixed. Transfer has improved fee collection and maintenance where WUAs had real authority, financial autonomy, reliable water supply from the main system and support, and where farmers saw clear benefits. It has failed where associations were created on paper, captured by elites, or given responsibility without control of water. Elinor Ostrom's design principles for long-enduring common-pool resource institutions -- clear boundaries, rules matched to local conditions, participation in rule-making, monitoring, graduated sanctions, conflict-resolution mechanisms, recognition of the right to organise, and nested enterprises -- were derived partly from studies of farmer-managed irrigation systems, such as those in Nepal and Spain, and remain a useful checklist (see Natural Resource and Environmental Economics).
About 300 river basins and many aquifers are shared by two or more countries, covering a large part of the Earth's land surface and population. River basin organisations coordinate management within and between countries: examples include the Murray-Darling Basin Authority in Australia, the Mekong River Commission (established by the 1995 Mekong Agreement among Cambodia, Laos, Thailand and Viet Nam), the Nile Basin Initiative (1999), and the International Commission for the Protection of the Rhine.
Two global conventions codify customary international water law. The UN Watercourses Convention (1997, in force since 2014) sets out the principles of equitable and reasonable utilisation, the obligation not to cause significant harm to other watercourse states, and the duty to exchange information and give prior notification of planned measures. The UNECE Water Convention (1992), originally for Europe, was opened to all UN members in 2016 and has since been joined by countries in Africa and elsewhere. Most practical cooperation, however, rests on basin-specific treaties. Research on transboundary basins shows that cooperation is far more common than violent conflict, but tensions rise where upstream development, such as large dams, changes flows without agreement, as in the Nile basin over the Grand Ethiopian Renaissance Dam.
The Indus Waters Treaty (1960), brokered by the World Bank, allocated the three eastern rivers (Ravi, Beas and Sutlej) to India and the three western rivers (Indus, Jhelum and Chenab) largely to Pakistan, with India permitted limited non-consumptive uses such as run-of-river hydropower on the western rivers; it survived several wars and has dispute-resolution mechanisms, though disputes over projects have recurred and India announced in 2025 that it was holding the treaty in abeyance. The Ganges Water Treaty (1996) between India and Bangladesh shares dry-season flows at Farakka for thirty years. Cooperation with Nepal (Kosi and Gandak agreements, the Mahakali Treaty of 1996) and Bhutan (hydropower) is also important, as are data-sharing arrangements with China on the Brahmaputra.
Within India, rivers flowing through several states give rise to inter-state disputes, adjudicated under the Inter-State River Water Disputes Act 1956 by tribunals; the long-running Cauvery dispute among Karnataka, Tamil Nadu, Kerala and Puducherry led to a tribunal award (2007), a Supreme Court judgment (2018) and the creation of the Cauvery Water Management Authority. Basin-level planning in India is weak because water is primarily a state subject under the Constitution; proposals for river basin authorities and a national framework law aim to strengthen it. River interlinking proposals raise major ecological, social and inter-state questions.
Agri-food companies depend on water throughout their supply chains -- most of their water footprint lies in irrigated ingredients rather than in factories -- and face physical risks (droughts, floods, depletion), regulatory risks (allocation cuts, abstraction charges, pollution rules) and reputational risks (conflicts with communities over water). Water stewardship means using water in a way that is socially equitable, environmentally sustainable and economically beneficial, achieved through a stakeholder-inclusive process that includes site- and catchment-based actions. It goes beyond efficiency inside the factory fence to collective action in the catchment.
Tools support this. The CEO Water Mandate (launched by the UN Global Compact in 2007) commits companies to water stewardship principles and publishes guidance on collective action and context-based targets. CDP's water security questionnaire asks companies to disclose water risks, use and governance, and investors use the results. Risk-mapping tools, such as WRI's Aqueduct atlas, identify sourcing regions with high baseline water stress, depletion, flood or drought risk. The Science Based Targets Network has published methods for setting freshwater targets for quantity and quality in priority basins.
The Alliance for Water Stewardship (AWS) Standard (version 2.0, 2019) is the main certifiable standard for sites, including farms and food factories. It requires a site to follow five steps -- gather and understand; commit and plan; implement; evaluate; communicate and disclose -- and to pursue five outcomes: good water governance, sustainable water balance, good water quality status, healthy status of important water-related areas, and safe water, sanitation and hygiene for all. Certification is by accredited third-party auditors, with core and advanced levels.
Companies increasingly make claims such as 'water neutral' or 'water positive', promising to replenish more water than they use, often through watershed projects. Such claims need care: water is local, so replenishment should occur in the same catchment and matter there; volumetric water benefit accounting methods (developed by WRI and partners) set out how to estimate benefits, but restoring a wetland in one basin does not offset depletion in another. Credible corporate programmes target the basins where their sourcing creates real risk and impact, engage suppliers on irrigation efficiency with consumption caps, support basin governance and data, and report transparently. Agricultural supply-chain programmes often combine stewardship with soil health and nutrient management, linking water quantity and quality.
Master the indicators (Falkenmark thresholds, withdrawal-to-availability, SDG 6.4.1 and 6.4.2), the water productivity and Ky equations, footprint arithmetic including grey water, groundwater stage-of-extraction categories, harvesting volumes and SAR. Understand the irrigation efficiency paradox, virtual water and its limits, the Dublin Principles and IWRM, water rights doctrines, PIM, the UN Watercourses Convention, the Indus and Ganges treaties, and the AWS Standard. Practise writing balanced answers on contested issues such as river interlinking and groundwater regulation, citing evidence on both sides and the interests of different users.
As an irrigation or watershed officer, groundwater hydrologist, basin planner or corporate water analyst you assess water balances, design and evaluate harvesting and recharge works, promote micro-irrigation with sensible safeguards, support water user associations, calculate footprints and risk scores for sourcing regions, and prepare sites for AWS certification. You must translate between engineers, farmers, regulators and managers, and judge whether claimed water savings are real at basin scale. Good record-keeping, field measurement and simple water balances are your main tools.
As a secretary of water resources, basin authority head, development-bank water lead or head of corporate sustainability you set allocation and groundwater policy, negotiate between states or countries, decide on large investments in storage, recharge, reuse and canal modernisation, reform power and crop subsidies that drive depletion, and design corporate water targets that address real catchment risks. You balance food security, farm incomes, urban demand, ecosystems and political feasibility, and must be able to explain trade-offs to ministers, farmers and the public.
As a researcher you work on basin water accounting and remote sensing of evapotranspiration, the irrigation efficiency paradox, groundwater modelling and governance, the hydrological effects of harvesting and recharge at scale, wastewater reuse risks including emerging contaminants, water markets and rights, transboundary cooperation and conflict, and the evaluation of stewardship programmes. You advise governments and international bodies, contribute to basin plans and global assessments, and train the next generation of hydrologists, engineers, economists and water governance professionals in many countries.
Global figures (shares of withdrawals, groundwater use, virtual water volumes) are approximate and vary by source and year. The manual does not cover irrigation and drainage engineering, pump selection, canal design or detailed groundwater hydraulics (see Agricultural Engineering and Hydrology and Water Resources), nor water pricing economics (Natural Resource and Environmental Economics). Country water law is summarised through examples, not comprehensively; Indian state groundwater laws, interstate tribunal awards and transboundary developments (including the status of the Indus Waters Treaty after 2025 and the Ganges Treaty's renewal in 2026) change and should be checked. Desalination, urban water supply and flood management are outside its scope.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions. Every numerical answer was computed by script; Thresholds, coefficients and volumes are stated in each stem because they differ between sources, basins and countries.
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