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Data centers use water mainly to remove heat from servers, but the amount depends on the facility’s cooling design, operating conditions, climate, and electricity supply. A single water-use number—or a label such as “liquid-cooled”—cannot show a project’s full local impact. Residents evaluating a proposal should ask for projected annual and peak-day withdrawals and consumption, the water sources, cooling and heat-rejection systems, drought plans, and enforceable monitoring and reporting.
How do data centers use water?
Servers turn electricity into computing work and heat. A data center’s cooling system moves that heat away from IT equipment so the facility can operate within its required conditions. Water may carry heat through the building, absorb it in a cooling tower, or enter the facility as makeup water to replace water lost during cooling. Some designs use little or no water on site for cooling; others rely on evaporation and need a continuing water supply.
The U.S. Department of Energy’s Federal Energy Management Program (DOE FEMP) describes a common evaporative cooling arrangement as a sequence of heat transfers:
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- Room cooling equipment removes heat from the data-center space and transfers it to a chilled-water loop.
- Chillers move that heat from the chilled-water loop to a condenser-water loop.
- The condenser-water loop carries heat to a cooling tower. Some of its water evaporates, releasing heat to the atmosphere.
- Makeup water replaces the evaporated water. Some water is also discharged as blowdown to control the dissolved minerals that build up as water circulates and evaporates.
Evaporation is central to the water demand of this common arrangement: water that evaporates is not available to circulate again in the system. Blowdown is different from evaporation because it is a liquid discharge, but it still affects the facility’s water balance and needs a management plan.
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What “liquid cooling” does—and does not—tell you
Direct liquid cooling transfers heat from IT equipment into a recirculating chilled-water loop. That describes how heat leaves the equipment; it does not, by itself, tell you how heat will be rejected outside the building. The downstream system may still use a cooling tower and evaporate water. Ask about the full cooling train, including heat-rejection equipment, rather than treating “direct liquid cooling” as a complete water-use specification.
Other systems can shift demand between water and energy. LBNL’s 2024 U.S. data-center energy report says air-cooled chillers use no water but more energy, while water-cooled chillers and other evaporation-based systems are generally more energy efficient. Neither “water-free” nor “water-efficient” alone settles which option is preferable: the comparison also depends on electricity use, the water implications of electricity generation, local water conditions, and performance during hot weather.
Why is there no single data-center water-use figure?
Water demand depends on the facility’s IT heat load, cooling design, operating practices, climate, and other site conditions. Even facilities with similar names or capacities may use different cooling systems or operate them differently. A figure without a defined boundary and period can conceal whether it means water taken from a source, water consumed, water used only for cooling, or a broader footprint that includes electricity generation.
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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsA June 2025 Lawrence Berkeley National Laboratory (LBNL) workload-level study reported more than a 10,000-fold variation in water use across the workloads it assessed. The authors attributed this to more than 1,000-fold differences in water consumption per kilowatt-hour of server electricity and approximately tenfold differences in server workload efficiency. This is a finding about workloads, not evidence that facilities in a particular community necessarily differ by that factor.
The study identifies several contributors to workload-level variation: server efficiency and utilization, the share of inactive servers, cooling-system and infrastructure efficiency, climate, electricity-grid water factors, and server refresh cycle. The practical implication is that a number from another facility or a general benchmark cannot substitute for a project-specific estimate with stated operating assumptions.
Ask for withdrawals and consumption separately
A withdrawal is water taken from a source, such as a municipal system, groundwater, or surface water. Consumption refers to the portion not returned to the source in a usable form over the relevant place and time; evaporation is one route by which water is consumed. These are related but not interchangeable measures. Ask for both, with units, time periods, source breakdowns, and the methods used to estimate them. Annual totals show overall demand; peak-day estimates help reveal pressure during the periods when local systems may be most constrained.
Understand WUE’s boundary
Water usage effectiveness (WUE) is commonly expressed as annual site water use divided by IT equipment energy use, often in liters per kilowatt-hour. It can help compare facility-level water use relative to IT energy, but a WUE figure is only as informative as its measurement boundary, reporting period, and denominator. Ask what water is included in “site water,” what IT energy is included in the denominator, and whether the reported value is measured or projected.
LBNL’s 2024 report distinguishes site water consumption, primarily associated with cooling infrastructure, from source water consumption associated with electricity generation. Site WUE does not by itself include the water consumed to produce the electricity the data center uses. If a project publishes only a site figure, ask whether it will also estimate electricity-related water use and explain the method. Keep the two measures distinct rather than adding them without a consistent accounting boundary.
How should residents compare cooling proposals?
If a project offers multiple cooling options, compare the same dimensions for each option and request assumptions in writing. A claimed improvement in one metric may shift impacts to another part of the system. For example, a cooling option that reduces direct water use can require more energy, while evaporative cooling can reduce energy demand but require makeup water and create blowdown.
| Comparison point | What to request or examine |
|---|---|
| Water demand | Annual and peak-day withdrawals and consumptive use, reported separately |
| Water source | Volumes from potable groundwater, surface water, reclaimed municipal wastewater, or other sources |
| Cooling and heat rejection | Cooling equipment, downstream heat-rejection method, and conditions under which water is used |
| Electricity-related water | Whether source water associated with electricity generation is estimated, and how |
| Reuse feasibility | Reclaimed-water supply, treatment requirements, connection infrastructure, and seasonal availability |
| Discharges and residuals | Blowdown, concentrated brine, salts, and other treatment residuals, including their destinations and permits |
| Local resilience and accountability | Drought response, monitoring frequency, public reporting, approved limits, and consequences for exceeding them |
DOE’s 2026 data-center FAQ says advanced technologies can sometimes reduce water needs by more than 90%. That is a potential for some applications, not a guaranteed saving or a universal comparison. For a proposed facility, ask what baseline the estimate uses, which technology and operating conditions it assumes, and whether the reduction is projected or demonstrated for the project.
Can reclaimed water reduce pressure on drinking-water supplies?
Reclaimed water can reduce reliance on potable supplies, but it does not make a project water-neutral or automatically solve local impacts. The available source, seasonal supply, treatment needs, distance to the facility, connection infrastructure, residuals, and discharge rules all matter. A useful proposal identifies the water source and volumes, explains how it will be treated and delivered, and accounts for what leaves the treatment and cooling systems.
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The U.S. Environmental Protection Agency’s Quincy case study, published in 2023, describes a reuse utility developed through a partnership between Microsoft and the City of Quincy. The utility treats cooling water from a Microsoft data center and recirculates it, reducing dependence on potable groundwater. EPA lists a project highlight of 138 million gallons (522 million liters) per year in demand offset. That is a case-specific figure, not a standard saving for data centers generally.
EPA also reports that the system uses 260 million gallons (984 million liters) per year of Columbia Basin Project water, primarily during summer, as makeup water. The case describes a small remaining potable-groundwater share at the time covered, treatment of mineral-rich blowdown, and management of concentrated residuals. EPA notes permits related to sludge and brine management, and explains that additional discharge permits would be needed for certain other uses or discharges.
The example illustrates why “recycled water” is not a complete account of a project’s water effects. Residents can ask where the supply originates, how much is available during the dry or high-demand season, what treatment and conveyance infrastructure is required, how concentrated residuals are handled, and which permits govern any discharge. The Quincy details are specific to that utility and the case-study period; they do not establish current conditions or permit requirements elsewhere.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should local residents ask about a proposed data center?
Bring specific, answerable questions to the project applicant, local utility, planning authority, and water-resource agency. Ask that estimates and commitments be documented in applications, permit conditions, or public reporting plans where applicable.
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Demand and source
- What are projected annual and peak-day water withdrawals and consumptive use, stated separately?
- What is the projected demand during hot weather, peak operations, and other high-demand periods, and what outdoor-temperature and workload assumptions support it?
- Which sources will supply the facility? How much will come from potable groundwater, surface water, reclaimed municipal wastewater, or another source?
- Are the figures measured or modeled? What system boundaries, units, and reporting periods do they use?
Cooling and electricity
- What cooling system will be installed, including the equipment that rejects heat from the facility?
- Under what seasons, outdoor temperatures, and workload levels will the system use water?
- Will the operator publish site water data monthly or annually, and define the WUE numerator, denominator, and boundary?
- Will electricity-related water use also be estimated? If so, what grid and accounting method will be used?
Reuse, drought, and residuals
- Could the facility use reclaimed water? Where would that water come from, what treatment is needed, and what pipes or other infrastructure must be built?
- How would drought or water restrictions affect the facility? What priority rules would apply to households, agriculture, and the data center?
- How will blowdown, concentrated brine, salts, and other treatment residuals be handled, and what permits cover their treatment, transport, or disposal?
Permits and accountability
- Which water-right, withdrawal, wastewater, land-use, and environmental approvals apply? Where can residents review the applications and permit conditions?
- Who will monitor compliance, how often will results be reported, and where will the public find the data?
- What happens if actual withdrawals, consumption, or discharges exceed an approved limit or a public commitment?
Permit names, disclosure rights, review procedures, and public-comment periods depend on the location and the project record. Residents should confirm applicable processes with the relevant local and state or regional authorities rather than assume one jurisdiction’s rules apply elsewhere.
How to judge the answers
Useful responses specify quantities, periods, sources, assumptions, and accountability. “Low water use,” a single annual total, or a WUE value without its boundary does not answer whether demand will coincide with local scarcity or how performance will be checked. A robust comparison puts the project’s annual and peak-day water use beside its source mix, cooling assumptions, drought provisions, discharge plan, and electricity-related water estimate.
Also distinguish a design promise from an enforceable condition and from an operating result. Ask which commitments appear in permit conditions or other binding approvals, who verifies them, how often the public receives results, and what remedy follows if a limit is exceeded. DOE’s 2026 FAQ states: “Not all data centers are the right fit for every location or community, and Tribes can and should decide for themselves whether data center projects align with their goals.” The guidance is specifically framed for Tribal economic development; it underscores that local decision-making should account for community priorities, rather than presuming every project is a fit.
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