Some data centers use water that evaporates in cooling towers to carry heat away from servers; others use different or hybrid systems, and a “liquid-cooled” design can still rely on a cooling tower. A facility’s actual water impact depends on its cooling equipment, computing load, water source, local supply conditions, and discharge arrangements. Residents evaluating a proposal should ask for both efficiency metrics and project-specific water volumes—including peak demand, source, consumption, discharge, and public reporting.
How data centers use water to cool servers
Servers and other information-technology equipment generate heat while operating. In a common cooling arrangement described by the U.S. Department of Energy’s Federal Energy Management Program (DOE FEMP), cooling equipment transfers heat from the data hall into water loops. The warmed water carries heat to a cooling tower, where some water evaporates into the air and removes heat from the remaining circulating water. That cooled water returns to the system to collect more heat.
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A cooling tower also needs blowdown: some circulating water is discharged so dissolved minerals do not build up excessively as evaporation concentrates them. A smaller quantity can leave as drift—tiny water droplets carried out of the tower with its exhaust air. Evaporation, blowdown, and drift are different parts of the water balance; asking only how much water is “used” can obscure where it goes.
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DOE FEMP describes cooling-tower use as tied to heat load and the efficiency of each heat-removal step. In practical terms, cooling demand is continuous when the facility is operating, but water needs are not a fixed amount per building or per server. They can change with IT workload, outdoor conditions, equipment design, and operations.
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Withdrawal, consumption, and discharge are not interchangeable
- Withdrawal or supply: water taken from a source or delivered to the facility. A project may report this as water supplied or make-up water added to its cooling system.
- Consumption: water that is not returned to the same water system in the same condition or time period. Evaporation is a key example in a cooling tower.
- Discharge: water released from the facility, including cooling-tower blowdown or other wastewater. Its volume, treatment, destination, and quality matter.
These figures answer different questions. A community weighing a project’s effects on local availability needs to know the proposed source and withdrawals; assessing water that will not return requires consumption estimates; understanding wastewater effects requires discharge volumes, treatment, and destination.
What cooling design is proposed—and does it evaporate water?
There is no single cooling design used by every data center. A proposal may use an evaporative cooling tower, air-side economizing, water-side economizing, direct liquid cooling, or a hybrid arrangement. Ask the developer to describe the system and its operating modes rather than relying on a broad label.
| Design or term | What it means for the heat path | What residents should establish |
|---|---|---|
| Evaporative cooling tower | Heat is rejected in part by evaporating water from the tower. | Ask for annual and peak make-up water, expected evaporation, blowdown, drift, and operating schedule. |
| Air-side economizing | Under suitable conditions, outside air can help reduce reliance on mechanical cooling. | Ask when it can operate in the local climate, what equipment remains in use, and how the mode affects water and energy use. |
| Water-side economizing | A water loop can provide cooling under suitable conditions while reducing use of mechanical cooling equipment. | Ask what water circuits and heat-rejection equipment are involved; the term alone does not establish whether water is consumed. |
| Direct liquid cooling | Liquid carries heat away from IT equipment into a circulating loop. | Ask where heat goes after it reaches that loop. DOE notes some direct-liquid configurations still reject heat through a cooling tower. |
| Hybrid system | More than one cooling approach or operating mode may be combined. | Ask which mode runs in which conditions and request water estimates for each mode and for the facility overall. |
“Liquid cooled” does not by itself mean “no evaporative water use”: the liquid may simply move heat to another part of the cooling system, and some configurations still use a tower to reject that heat. Likewise, a system name does not tell a resident whether cooling towers operate year-round, what portion of demand they serve, or how often economizing is possible.
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There is no defensible universal water-use figure for a data center based on the information available here. The project-specific examples below illustrate why the unit, time period, phase, and source of an estimate must travel with the number.
| Published figure | What it applies to | Important qualification |
|---|---|---|
| 23 acre-feet of potable water per year | City of Gilroy’s expected initial-phase demand for the AWS data-center project. | The city says it updated the figure on August 12, 2026, to align with the environmental review. It is a project-specific estimate, not a general benchmark. |
| 4,000 gallons per day | Town of Tyrone, Georgia, reports this as Microsoft’s estimate for its facility once operational. | The town says construction demand would be higher. This estimate applies to that project, not data centers generally. |
A useful proposal should give estimates for initial operations and full build-out, not just a single annual average. Request annual, monthly, and maximum-day demand, along with assumptions about occupancy, computing load, cooling design, and seasonal conditions. Averages can conceal short periods of higher demand that matter to a utility or water system.
What WUE can tell you—and what it cannot
Water usage effectiveness (WUE) is a site water-use intensity metric: annual site water use in liters divided by IT equipment energy use in kilowatt-hours. It helps compare water use relative to computing energy, but a ratio is not a complete account of a facility’s local impact. It does not, by itself, tell residents the total volume used, maximum-day demand, water source, or effect on a particular supply.
Ask the developer to report WUE and absolute water volumes together, and to define what it counts as site water use and IT energy use. The National Laboratory of the Rockies data center is a DOE FEMP case study from 2019 reporting a power usage effectiveness (PUE) of 1.06 and WUE of 0.7 for its hybrid cooling system. Those figures describe that case study; they are not typical-facility values or guaranteed outcomes for a proposed project.
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Questions residents can ask about a proposed project
The following questions are a practical way to seek project-specific information. They are not a universal legal checklist: applications, approvals, public-comment periods, and reporting requirements vary by state and locality.
1. How much water will the facility need at each phase?
- What are projected annual, monthly, and maximum-day volumes for initial operations and full build-out?
- What assumptions underlie each estimate—occupancy, computing load, cooling design, weather, and operating schedule?
- Will the developer publish actual water use after opening, and how often?
Request a distinction between water supplied, consumed, and discharged, rather than accepting one undifferentiated “water use” number.
2. Where will the water come from?
- Will the project use potable municipal water, reclaimed wastewater, groundwater, surface water, or another source?
- Will the water source or delivery require new infrastructure, and who will provide it?
- What drought or shortage restrictions would apply, and how would the facility operate if supply were constrained?
Gilroy’s project page illustrates why both source and quantity need to be made explicit: its published figure is for potable water and applies to that project’s initial phase. It should not be treated as a prediction for a different site.
3. How much water will be consumed, discharged, and treated?
- What volumes are expected to evaporate, leave as blowdown, or be lost as drift?
- What wastewater will be produced, what treatment is required, and where will it be discharged?
- What monitoring will verify discharge volume and quality?
These questions make the facility’s water balance legible. A low discharge figure alone does not establish low demand if a larger share of supplied water evaporates.
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4. What equipment and operating modes are actually proposed?
- Can the developer provide a system diagram showing the data hall, cooling loops, towers, and water connections?
- Will cooling towers run year-round? If not, under what conditions do they run?
- When can air-side or water-side economizing reduce mechanical cooling, and does direct liquid cooling still depend on evaporative heat rejection?
Ask for water estimates by operating mode where feasible. That helps distinguish a design’s name from the equipment and operating conditions that determine its water pathway.
5. What measures will reduce water demand?
DOE FEMP identifies operating practices and equipment choices that can improve cooling efficiency, but actual performance depends on design and operation. Ask which measures the proposal includes and whether savings have been modeled for the local climate.
- Will operating set points or higher chilled-water temperatures reduce cooling requirements, and what local-condition assumptions support the estimate?
- Can air-side or water-side economizing be used, and how many operating hours are projected?
- What cycles of concentration will the cooling tower target, and how will water quality be managed?
- Will condensate or reclaimed water be reused, and what share of demand could it supply?
- What filtration or treatment is proposed, and how does it affect make-up water and blowdown?
DOE FEMP reported in 2019 that certain practices enabling higher chilled-water temperatures and reduced airflow can produce 20% less chiller energy, with associated reductions in cooling-tower heat rejection and water use. That is not a guaranteed saving for every facility. The same 2019 source reported 20% lower cooling-tower make-up water and 50% lower blowdown when cycles of concentration increase from three to six. Those are reported reductions under that specific operating change, not a promise of the same result at another site.
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Ask the local planning department and water utility which project applications, public hearings, comment periods, water approvals, and reporting obligations apply to this proposal, and where the official record can be reviewed. Do not assume that a process or threshold used in another town applies locally.
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Current official examples show how requirements differ. Utah’s Division of Water Rights describes rules for qualifying new large data-center projects over 10,000 square feet that intend to draw at least 75 acre-feet of water annually; its page says reporting requirements are effective July 1, 2026. Whether those criteria and requirements apply to a particular project depends on current law and its circumstances. Hayward’s application process and Tyrone’s project approvals are other jurisdiction-specific examples, not templates for every community.
7. Who reviews estimates and checks actual use?
- Will the water utility or regulator review the developer’s demand assumptions?
- Will actual withdrawals, consumption, and discharges be made public, and how often will reporting occur?
- What happens if actual use exceeds the approved projection?
- Are water commitments enforceable conditions or voluntary company pledges?
A projection is more useful when the public can see how it was calculated and compare it with measured use after opening. Ask who is responsible for measurement, review, publication, and follow-up if real demand differs from the estimate.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to compare cooling alternatives without reducing the choice to one metric
If a proposal presents more than one cooling option, compare them against the same local conditions and project scale. No single efficiency number captures water availability, energy, wastewater, reliability, and enforceability all at once.
| Comparison area | What to compare | Why it matters |
|---|---|---|
| Water demand | Annual and peak consumptive use, plus supplied or withdrawn volumes. | Peak demand and total volume can matter even when an intensity metric appears favorable. |
| Source and scarcity | Source-water type and local supply conditions, including drought constraints. | The same volume can have different consequences depending on where it comes from and competing local needs. |
| Discharge | Volume, quality, treatment, destination, and monitoring. | Water returned to a system is not necessarily returned in the same condition or to the same place. |
| Energy and reliability | Energy requirements and operating reliability under local climate conditions. | Water and energy effects can move together or involve trade-offs; a water-only ranking may miss them. |
| Cost and implementation | Capital and operating implications of each proposed alternative. | A design’s projected performance depends on equipment, maintenance, and operating choices. |
| Accountability | Public measurement, reporting frequency, independent review, and enforceability. | Promises are easier to evaluate when there are defined metrics, public records, and a response to exceeding projections. |
DOE FEMP reported in 2019 that its National Laboratory of the Rockies case study combined a hybrid cooling system with PUE of 1.06 and WUE of 0.7. It is an example of one facility, not evidence that a particular technology will deliver the same result elsewhere. Ask developers to provide project-specific modeled performance and disclose assumptions rather than treating another facility’s figures as a forecast.
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