How much water does a data center use? It depends on one choice.

• Open cooling towers (evaporative): warm water is sprayed through outdoor towers; evaporation carries the heat away. Energy-efficient, but the thirstiest design: roughly 6.75 million gallons per year per megawatt, per Uptime Institute.¹⁰⁰ Some water is also regularly discharged to the sewer as “blowdown” to flush out concentrated minerals.¹⁰¹
• Air-cooled (dry) systems: giant radiator-and-fan units reject heat straight to the air. Near zero water, but more electricity (evaporative assist can cut peak-summer cooling electricity 10–35%) and more fan noise.¹¹⁴
• Direct evaporative (“swamp cooler”): outside air is cooled through wetted media. Uses far less water than open towers; Meta’s version runs about a tenth of traditional consumption.¹⁰⁰
• Adiabatic / hybrid: dry coolers that mist water only on the hottest days. Low, seasonal water use.¹⁰⁰
• Closed-loop, direct-to-chip liquid cooling: the new AI-era standard. A sealed water loop is filled once at construction and recirculated indefinitely; Microsoft says its zero-water-for-cooling design avoids more than 125 million liters (~33 million gallons) per facility per year, leaving only restroom-scale water use.¹⁰²
• Immersion cooling: servers submerged in non-conductive fluid; essentially no on-site water. Still niche (crypto, HPC).¹⁰⁰

Using published water-efficiency figures (WUE: liters of water per kilowatt-hour of computing), here is the computed range for a 30 MW facility running at full load. These are estimates from cited inputs, not the developer’s numbers; the actual figure depends entirely on the cooling design the end user chooses.

Math: 30 MW × 8,760 hours = 262.8 million kWh/yr; multiply by the cited WUE and convert liters to gallons. WUE inputs: Uptime Institute,¹⁰⁰ industry average,¹⁰⁰ Microsoft,¹⁰² Meta.¹⁰³ The closed-loop row uses Microsoft’s real Wisconsin facility: 2.8M gallons/yr in Phase 1, ~8.4M gallons/yr at later phases.¹⁰⁸

For comparison: Google disclosed that its average data center campus used about 450,000 gallons per day in 2021¹⁰⁴, so a worst-case evaporative 30 MW build would behave like a typical Google campus, while a closed-loop build would use about as much water as a large office park.¹⁰⁸

Water and electricity trade against each other. Evaporating water is the cheapest way (in energy) to shed heat; going dry costs more electricity.¹¹⁴ Google has argued water-cooling cuts its energy use about 10% versus air cooling.¹⁰⁴ There’s also a hidden ledger: peer-reviewed research found that roughly 75% of data centers’ total water footprint is indirect: consumed by the power plants generating their electricity, not at the site itself.¹⁰⁵ A “zero-water” data center still drives water use somewhere on the grid. Nationally, data centers consumed about 66 billion liters (~17 billion gallons) directly in 2023, a figure the federal LBNL report projects could double or quadruple by 2028.¹² The industry trend helps here: AI chips run too hot for air alone, so new builds increasingly use sealed direct-to-chip loops, which happen to nearly eliminate on-site water use.¹⁰²

Nearly all electricity entering a data center leaves as heat, so a 25–30 MW facility is also, in effect, a 24/7 heat source of roughly the same size. In Northern Europe, where cities have district heating networks, that heat genuinely warms homes: Meta’s Odense, Denmark plant recovers heat for the city network (about 45 MW of heat production serving thousands of homes and a hospital),¹²⁶ Microsoft’s data centers near Helsinki now supply up to 180 MW of district heat, on track to cover ~40% of heating demand for an area of 250,000 people,¹²⁷ Google’s Hamina facility will cover up to 80% of its town’s heating demand free of charge,¹²⁸ and Stockholm’s utility literally pays data centers for their heat.¹²⁹ Germany now requires new data centers to reuse 10–20% of their energy as heat.¹³⁵

The honest catch: data center exhaust is low-grade heat, roughly 100°F air from air-cooled halls (hotter, more usable 50–60°C water from modern liquid-cooled designs),¹³⁴ and using it requires heat pumps plus, crucially, a heat customer nearby. The Nordic projects work because city-wide hot-water networks already existed; almost no U.S. town has one,¹³³ and we found no documented example of a small-city American data center heating homes.

What is precedented in the U.S. is single-neighbor reuse: Amazon’s Seattle towers are warmed by ~5 MW of waste heat piped across the street from a data-dense building,¹³⁰ Notre Dame’s server racks heat South Bend’s municipal greenhouse, saving the city about $70,000 a year,¹³¹ and in the UK a 28 kW micro data center cut a public swimming pool’s gas bill 62%.¹³² A regional policy group, ReImagine Appalachia, argues for exactly this model here: using data center heat for schools, public buildings, or greenhouses on former mine land.¹³⁶ For Pikeville, heating the town is not realistic; heating an adjacent greenhouse complex, pool, or campus building is, if heat-recovery plumbing is designed in from day one, which is a reasonable thing to raise while a Development Agreement is still being negotiated.

• The Dalles, Oregon: Google’s data centers used 355.1 million gallons in 2021 (29% of the entire city’s water), a fact disclosed only after a 13-month public-records fight with the local newspaper.¹⁰⁶ Google also funded $28.5 million of city water infrastructure.¹⁰⁷ Lesson: the problem wasn’t only the volume; it was the secrecy.
• Newton County, Georgia: residents 1,000 feet from Meta’s construction site reported wells running dry and sediment; Meta’s commissioned study found no connection, the county did no pre-construction well survey, and causation remains unresolved.⁸⁶
• Mesa & Goodyear, Arizona: desert cities negotiated tiered water caps (1 up to 4 million gallons/day in Mesa)¹⁰⁹ and in Goodyear, Microsoft agreed to switch its design to air cooling and contributed $36M toward a wastewater plant.¹¹⁰
• Memphis: xAI pledged an $80M wastewater recycling plant (13 million gallons/day design) to stop drawing on the drinking-water aquifer. Groundbreaking happened, though the project was later paused, a reminder that pledges need enforceable timelines.¹¹¹
• Mount Pleasant, Wisconsin (the quiet success): Microsoft’s closed-loop campus uses 2.8M gallons a year in Phase 1, less than many ordinary industrial customers on the same utility.¹⁰⁸
• Loudoun County, Virginia: the water utility delivers reclaimed (treated wastewater) through purple pipe for data center cooling (over 750 million gallons in 2025), sparing the same volume of drinking water.¹¹² Google’s Georgia site similarly cools with recycled municipal effluent.¹¹³

Evaporative cooling doesn’t just take water in; it sends some back. Because evaporation leaves minerals behind, the recirculating water steadily concentrates dissolved solids (calcium, magnesium, chloride, silica), and a portion is periodically flushed out as blowdown. To keep the towers themselves healthy, water-treatment vendors also dose the loop with chemicals (biocides to control bacteria and algae, plus scale and corrosion inhibitors), and EPA’s own guidance notes that discharged water must still meet water quality standards.¹⁰¹ A 2026 UC Berkeley law school report states it directly: data centers can affect water resources “by discharging wastewater that contains concentrated minerals, chemical additives, and other pollutants into surface water or groundwater supplies.”¹¹⁷ Closed-loop designs largely sidestep the issue: a sealed loop is filled once, so there is no routine blowdown to dispose of.¹⁰²

Two legal paths govern that discharge. If blowdown goes to the city sewer (the common case), the wastewater utility regulates it under the federal pretreatment program, which exists precisely to keep industrial discharges from overwhelming a treatment plant or passing through it untreated.¹¹⁸ If a facility discharges directly to a creek or river instead, it needs its own Clean Water Act (NPDES) permit, with numeric limits on what comes out, temperature and pH included, plus monitoring and public reporting.¹¹⁹

The track record, with names attached:

• Quincy, Washington (the clearest documented case): mineral-rich cooling discharge from data centers strained the city’s wastewater plant, which was never designed for it, and pushed dissolved-solids levels past the state’s 500 mg/L guideline for water recharged into the aquifer. The fix: Microsoft paid the entire $31 million cost of a dedicated water-reuse utility (operational in 2021, run by the city under a 30-year agreement) that now treats and recycles about 138 million gallons of cooling water a year instead of discharging it.¹²⁰ The problem was real and the problem was fixable; the question was who pays.
• The Dalles, Oregon (the disclosure problem): the Columbia River Inter-Tribal Fish Commission told the Oregon governor’s data center task force in 2026 that discharges can add thermal stress to a river that has already lost nearly 80% of its salmon runs, and could contain chemicals, including PFAS and biocides, many of which aren’t disclosed, with “virtually no emergency planning” for spills.¹²¹ These are concerns about what could be in the water, raised because nobody outside the companies knows the chemical list.
• Georgia (the contested case): the Newton County well complaints described above escalated: after residents’ jars of discolored water reached a May 2026 congressional hearing, EPA directed its regional office to gather information from Georgia regulators, while stressing this is fact-finding, not a formal investigation. Meta points to the groundwater study it commissioned, which found no link to its construction, and notes its operating water comes from the county utility.¹²² The dispute is hard to resolve partly because nobody tested the wells before construction began.⁸⁶

The other contamination pathway has nothing to do with cooling: fuel. Backup generators mean diesel stored on site, and EPA calls leaking underground storage tanks “a common source of groundwater contamination”; petroleum contains benzene, a known carcinogen.¹²³ Federal rules require facilities storing oil to maintain spill-prevention (SPCC) plans designed to keep it out of waterways.¹²⁴ A 2026 fact-check that asked squarely “can data centers contaminate wells and other water sources?” answered yes, through diesel leaks or improper wastewater discharge, but if containment fails. We found no documented U.S. case of data center cooling discharge contaminating drinking water; the documented problems have been dissolved-solids loads on small treatment plants (Quincy), construction-era sediment disputes (Georgia), and secrecy about what’s in the water (The Dalles). The risk is a management and enforcement question, not an inevitability.¹²⁵