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Data centers use water mainly to remove heat, but how much they withdraw or consume depends on the cooling system, weather, workload, and water source. A facility’s annual water total or WUE score alone cannot show whether it is putting pressure on a local supply: you also need to know where its water comes from, what returns to the source, and what other people and ecosystems depend on that water.
How water is used to cool a data center
Servers produce heat that must be carried away to keep equipment operating. Facilities can combine air conditioning and fans, liquid coolant circulated through pipes or around components, evaporative cooling, and free cooling that uses favorable outdoor conditions to reduce mechanical cooling. The system’s water demand can vary with facility design, climate, humidity, workload, and operating choices. The UC Berkeley Center for Law, Energy & the Environment’s 2026 report describes these approaches and their tradeoffs.
In a cooling tower, warm water from the condenser loop releases heat as some of it evaporates. The tower also drains some water as blowdown to limit the buildup of dissolved minerals; replacement water, called makeup water, replenishes the system. Evaporation is the principal tower water loss. DOE guidance says that increasing a tower’s cycles of concentration from three to six can reduce makeup-water requirements by 20% and blowdown by 50%. These are operational guidance figures, not guaranteed savings for every tower or site. See the U.S. Department of Energy Federal Energy Management Program’s cooling-water guidance.
How cooling approaches trade water against energy
| Approach | Typical direct-water tendency | Important tradeoff or condition |
|---|---|---|
| Evaporative cooling | Can use substantial water because evaporation carries heat away. | Demand depends on climate, system design, and operation. |
| Air cooling | Generally uses less water on site. | May require more energy than water-intensive cooling. |
| Free cooling with outside air | Can use no water in the cooling process when conditions allow. | Availability depends on outdoor conditions; some indirect and hybrid designs have different water needs. |
| Liquid cooling | Can be water-efficient in a closed loop and may use fluids other than water. | “Liquid cooling” does not by itself specify the fluid, system design, or total water footprint. |
These are general tendencies, not a universal ranking: facilities combine technologies, and local weather and operating conditions affect performance. Lower on-site water demand can mean higher electricity use, shifting some water demand to power generation. The 2026 UC Berkeley report discusses this water-energy tradeoff.
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What water-use figures do—and do not—tell you
- Withdrawal is water taken into a facility, including water that may later be returned. Consumption is the portion not returned to its original source and therefore unavailable for reuse there. Discharged water may be treated; cooling-tower blowdown can contain concentrated minerals or additives. The distinction is set out in the UC Berkeley report.
- Direct water covers facility use such as cooling. Indirect water includes water used to generate electricity and in construction or supply chains. A facility-only figure does not capture all of these uses. Electricity source and location affect the indirect footprint, as explained in the Lawrence Berkeley National Laboratory’s 2024 U.S. data-center energy report.
- WUE, or water-use effectiveness, is an intensity ratio, not a water-stress or local-impact score. DOE Federal Energy Management Program guidance defines site WUE as annual site water use in liters divided by annual IT equipment energy in kilowatt-hours. Site WUE and source WUE account for different parts of the footprint; check which one a reported figure represents. See DOE’s WUE guidance and the LBNL report.
How to assess a data center’s local water impact
- Seek site-specific volumes. Ask for annual and peak-day withdrawals, consumption, and discharge, along with the water source. Request separate figures for potable, nonpotable, and recycled water where available, and establish whether each number is measured, projected, or actual for a stated reporting period. Aggregated company-wide totals do not establish the impact of one site.
- Trace the supply and return. Identify the supplying utility, surface-water basin, groundwater aquifer, or reclaimed-water system. Find out where discharge goes, how it is treated, and whether water returns to the same source in a usable condition.
- Put volumes in local context. Consider seasonal availability, drought and supply reliability, watershed or aquifer stress, infrastructure capacity, and existing residential, agricultural, ecological, and industrial demands. The same withdrawal can have different consequences in different places.
- Check the cooling system and its operation. Look for the system type, whether it is closed loop, tower makeup and blowdown, weather-related operating modes, and facility load. Confirm whether WUE is site-only or includes source water; do not treat it as a measure of scarcity.
- Consider discharge and electricity together. Examine blowdown quality and treatment as well as water used to produce the facility’s electricity. On-site cooling figures alone are not the full footprint.
- Evaluate mitigation in context. Potential measures include siting in cooler or lower-stress areas, using recycled or nonpotable supplies, adopting suitable closed-loop or low-water designs, adjusting temperature and humidity settings, using air-side economizing, and shifting workloads. Compare their effects on energy, reliability, and local infrastructure as well as water demand.
Why a precise local answer may be difficult to establish
The 2026 UC Berkeley report on California finds that site-level information is often sparse and that corporate disclosures may be voluntary and aggregated. Its recommendations include improved data collection, local decision support, efficiency and recycled-water measures, and more site-specific reporting; see the report summary. The report’s legal and regulatory discussion is California-focused. Water rights, utility arrangements, discharge permits, and land-use rules vary by jurisdiction, so its California findings should not be treated as a statement of requirements elsewhere.
Without facility-specific figures and local supply information, an exact impact cannot be inferred from a national estimate, a company total, or a WUE value. A sound assessment should identify what is known about the site and water system, and what remains unreported.
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