The interdependency
Why you cannot have energy security without water security
The water-energy nexus is one of climate change's most dangerous feedback loops: climate change reduces water availability → less water means less hydropower and constrained thermal plant cooling → energy shortages cause economic damage → slower energy transition → more climate change. Understanding this nexus is essential for both energy planners and water managers.
~4%
Global electricity consumed by water pumping + treatment
3–4 kWh/m³
Energy for SWRO desalination (most efficient)
41%
US freshwater withdrawals for thermoelectric cooling (USGS)
2022
Europe drought cut nuclear and coal output simultaneously
Water for energy production
How much water energy production actually uses
Thermoelectric cooling — the dominant water use:
Nuclear, coal, and gas power plants use the Rankine steam cycle — water is heated to steam, expands through turbines, then must be cooled back to liquid for the cycle to restart. This cooling requires enormous water flows. Two cooling methods: (1) Once-through cooling: draws river/lake/ocean water, heats it ~10°C, returns it to source. Withdraws 1,000–2,000 litres per MWh but consumes only ~10 litres (returns most). Restricted in drought or when river temperatures are already high. (2) Evaporative cooling towers: visible white plumes from nuclear and coal plants. Withdraws 500–1,000 litres per MWh but consumes 400–900 litres (evaporated). Less water-intensive to withdraw, more to consume. The 2022 European drought forced France's EDF to reduce nuclear output at multiple plants because the Loire (47.08°N 1.21°E), Rhône, and Garonne rivers were too warm — returning cooling water above the legally permitted river temperature limit. France's nuclear capacity dropped approximately 30% at peak summer 2022. Source: IAEA Nuclear and Water Security · EDF operational reports 2022.
Nuclear, coal, and gas power plants use the Rankine steam cycle — water is heated to steam, expands through turbines, then must be cooled back to liquid for the cycle to restart. This cooling requires enormous water flows. Two cooling methods: (1) Once-through cooling: draws river/lake/ocean water, heats it ~10°C, returns it to source. Withdraws 1,000–2,000 litres per MWh but consumes only ~10 litres (returns most). Restricted in drought or when river temperatures are already high. (2) Evaporative cooling towers: visible white plumes from nuclear and coal plants. Withdraws 500–1,000 litres per MWh but consumes 400–900 litres (evaporated). Less water-intensive to withdraw, more to consume. The 2022 European drought forced France's EDF to reduce nuclear output at multiple plants because the Loire (47.08°N 1.21°E), Rhône, and Garonne rivers were too warm — returning cooling water above the legally permitted river temperature limit. France's nuclear capacity dropped approximately 30% at peak summer 2022. Source: IAEA Nuclear and Water Security · EDF operational reports 2022.
Hydropower and drought — the new normal:
Hydropower provides approximately 16% of global electricity and approximately 60% of renewable electricity. But it is entirely dependent on precipitation and snowmelt. Climate change is causing: (1) More intense droughts reducing reservoir levels; (2) Shifting precipitation patterns — some regions getting wetter, others much drier; (3) Earlier snowmelt changing the timing of river flows. Lake Mead (36.02°N 114.73°W), the Colorado River reservoir serving Hoover Dam (2,074 MW) and millions in the US Southwest, fell to historically low levels in 2021–2022 (below 1,050 ft elevation — triggering Tier 1 and Tier 2 water shortage declarations). Brazil (88% hydropower) experienced severe droughts in 2001, 2012, 2021 — each time resorting to emergency fossil fuel or rationing. Southern Africa, China's Yangtze basin, and southern India have all experienced recent droughts that constrained hydro output. The IEA estimates that global hydropower generation will be increasingly variable due to climate — requiring additional storage and backup capacity. Source: Bureau of Reclamation Colorado River data · IEA Hydropower Special Report 2021.
Hydropower provides approximately 16% of global electricity and approximately 60% of renewable electricity. But it is entirely dependent on precipitation and snowmelt. Climate change is causing: (1) More intense droughts reducing reservoir levels; (2) Shifting precipitation patterns — some regions getting wetter, others much drier; (3) Earlier snowmelt changing the timing of river flows. Lake Mead (36.02°N 114.73°W), the Colorado River reservoir serving Hoover Dam (2,074 MW) and millions in the US Southwest, fell to historically low levels in 2021–2022 (below 1,050 ft elevation — triggering Tier 1 and Tier 2 water shortage declarations). Brazil (88% hydropower) experienced severe droughts in 2001, 2012, 2021 — each time resorting to emergency fossil fuel or rationing. Southern Africa, China's Yangtze basin, and southern India have all experienced recent droughts that constrained hydro output. The IEA estimates that global hydropower generation will be increasingly variable due to climate — requiring additional storage and backup capacity. Source: Bureau of Reclamation Colorado River data · IEA Hydropower Special Report 2021.
Desalination · GPS-located
Desalination — turning seawater into energy costs
Desalination is the most energy-intensive way to produce fresh water — and the most important for water-scarce regions. Global desalination capacity: approximately 100 million m³/day (2023, IDA). Two dominant technologies: SWRO (Seawater Reverse Osmosis) — forces seawater through semi-permeable membranes at 60–80 bar pressure; energy intensity 3–4 kWh/m³; has fallen dramatically from ~10 kWh/m³ in the 1990s due to energy recovery devices (ERDs) that recapture pressure from rejected brine. MSF (Multi-Stage Flash) — heats seawater to flash-evaporate fresh water through multiple pressure stages; energy intensity 10–15 kWh/m³ thermal + 3–4 kWh/m³ electric; older technology but produces very pure water. Named facilities: Ras Al Khair (27.10°N 49.50°E, Saudi Arabia, 1.025 billion litres/day = 1.025 Mm³/day, combined SWRO+MSF, ACWA Power, world's largest). Hassyan SWRO (25.00°N 55.24°E, Dubai, UAE, 818,000 m³/day). Sorek (31.94°N 34.74°E, Israel, 627,000 m³/day, IDE Technologies, world's largest SWRO when built 2013). Chennai SWRO (13.08°N 80.30°E, Tamil Nadu India, CMWSSB, 100 MLD — critical for Chennai which faces recurrent water crises). Nemmeli SWRO (12.82°N 80.30°E, Chennai, 100 MLD). Mumbai desalination (18.98°N 72.84°E, proposed 400 MLD — Mumbai faces critical water stress as Tansa and Vihar lakes age). The energy cost of desalination at scale is significant: Saudi Arabia's desalination plants consume approximately 25% of the kingdom's electricity — if Ras Al Khair runs on solar (as planned), this becomes a virtuous cycle. Source: IDA Desalination Yearbook 2024 · ACWA Power annual reports · CMWSSB Chennai.
Questions
Questions about the water-energy nexus
Will renewable energy reduce water stress — or create new water problems?
Renewable energy generally reduces water stress significantly, but not uniformly. Water reduction from renewables: Solar PV and wind turbines require essentially no water in operation — versus thermoelectric plants' hundreds to thousands of litres per MWh. The IEA estimates that the NZE 2050 transition would reduce global water withdrawals for electricity generation by approximately 85%. This is one of the largest co-benefits of the energy transition, particularly for water-stressed regions like the Middle East, India, and southern Europe. New water pressures from renewables: (1) Bioenergy requires water-intensive crops — sugarcane (Brazil), corn (USA), miscanthus, and eucalyptus require significant irrigation in some regions. BECCS (Bioenergy with CCS) at scale would require enormous land and water areas. (2) CSP (Concentrated Solar Power) uses wet cooling in many existing plants — consuming approximately 3 litres/kWh (similar to nuclear). Dry-cooled CSP reduces this but at some efficiency penalty. (3) Green hydrogen via electrolysis requires approximately 9 litres of water per kg of hydrogen produced — at the 5 MT/yr scale India targets, this is approximately 45 million tonnes of water per year (manageable, but significant in water-scarce regions). Net conclusion: Solar PV + wind + hydro is dramatically less water-intensive than fossil thermal for the same electricity output. The water-energy transition is strongly positive for global water security. Source: IEA Water-Energy Nexus 2016 · NREL Water Use for Energy in the United States · IRENA Renewable Energy and Water 2015.
Provenance
Attribution and citation
- Sources
- IEA Water-Energy Nexus 2016 · IDA Desalination Yearbook 2024 · USGS Water Use in the USA · Bureau of Reclamation Colorado River data · CMWSSB Chennai · EDF operational reports 2022
- Cite as
- "Water-Energy Nexus — How Water and Energy Depend on Each Other", The Energy Codex, https://thecodex.expert/energy/water-nexus/, last updated .