DATA CENTER COOLING

Data center cooling and water: evaporative vs. closed-loop cooling and WUE, explained

How data center cooling systems use water — evaporative towers, adiabatic coolers, closed-loop and liquid cooling — what water usage effectiveness (WUE) measures, and the water–energy trade-off behind each design.

By Argos Tellus · Updated October 1, 2026

KEY TAKEAWAYS

Evaporative cooling is the most water-intensive data center design: it rejects heat by evaporating water, which is consumed rather than returned. LBNL estimated about 1.8 liters of water per kWh of site energy for evaporatively cooled facilities.
Water usage effectiveness (WUE), defined by The Green Grid, is annual site water use divided by IT equipment energy, in liters per kilowatt-hour (L/kWh). Lower is better.
Closed-loop and direct-to-chip liquid cooling recirculate the same water and can nearly eliminate cooling-water consumption — Microsoft says its zero-water evaporative design saves more than 125 million liters a year per data center — but typically use more electricity.
Less on-site water often means more energy, and power plants consume water too. The right design depends on the local climate, power grid and, above all, the water source.
Cooling design changes how much water a site needs; it does not change whether the aquifer or utility beneath it can supply that water for decades.

Why data centers need cooling water

Nearly all the electricity a server uses ends up as heat, and that heat has to leave the building. AI accelerators concentrate far more power — and heat — into each rack than conventional servers, pushing operators toward cooling systems that move heat efficiently. In warm or dry climates, the cheapest way to reject heat to the atmosphere is to evaporate water.

At national scale, Lawrence Berkeley National Laboratory estimated that U.S. data centers consumed about 17 billion gallons of water directly in 2023, mostly for cooling (see how much water AI data centers use).

Data center cooling systems and their water use

Each architecture trades water for energy differently:

Cooling approach	How it rejects heat	On-site water use	Energy use
Evaporative cooling towers (with chillers)	Evaporates water in towers	High — continuous evaporation plus blowdown	Low to moderate
Direct / indirect evaporative (adiabatic) air cooling	Evaporates water into intake or heat-exchanger air	Moderate, mostly on hot days	Low
Air-side economization (“free cooling”)	Uses cool outside air directly	Very low	Very low in cool climates
Closed-loop with dry coolers or chillers	Recirculates water; rejects heat with fans or mechanical chillers	Near zero after initial fill	Higher, especially in hot weather
Direct-to-chip / immersion liquid cooling	Liquid at the chip carries heat to a closed loop	Near zero if paired with dry heat rejection	Efficient at high rack density

What WUE measures — and what it misses

The Green Grid defines water usage effectiveness as annual site water usage in liters divided by the energy consumed by IT equipment in kilowatt-hours. A WUE of 0 means no on-site water; evaporatively cooled facilities in hot climates run far higher than air- or closed-loop-cooled ones in cool climates.

WUE is useful for comparing designs, but it has blind spots. It is an annual average, so it hides summer peaks — exactly when local water supplies are tightest. Its standard form excludes the water consumed to generate the facility’s electricity. And it says nothing about where the water comes from: a liter of reclaimed wastewater and a liter pumped from a depleting aquifer count the same.

The water–energy trade-off

Cutting on-site water usually raises electricity use: dry coolers and chillers need more fan and compressor power than evaporative towers, particularly on hot days. Thermoelectric power plants also consume water for cooling, so on a fossil- or nuclear-heavy grid, saving water on site can partly shift consumption upstream. On a grid rich in wind and solar, which use very little water, the trade-off is more favorable.

That is why water-conscious operators combine strategies: closed-loop or liquid cooling for dense AI racks, economization where the climate allows, evaporative assist only during peak heat, and reclaimed or non-potable water where it is available.

Cooling design starts with the water source

Every cooling choice still needs a reliable water supply for initial fill, peak-day assist, humidification and people. For evaporative designs, that supply is large and continuous. Before choosing a design — and before buying the land — operators need to know whether the local utility or the aquifer beneath the site can sustain the facility’s peak demand for its full design life, without drawdown that harms neighboring wells.

The data center groundwater due-diligence checklist covers that assessment, and the cone of depression guide explains how a wellfield’s pumping spreads to neighbors.

Frequently asked questions

How do data centers use water for cooling?

Most water use comes from evaporative cooling: cooling towers or adiabatic coolers evaporate water to reject server heat to the atmosphere. The evaporated water is consumed. Some water is also discharged as blowdown to control mineral buildup.

What is water usage effectiveness (WUE)?

A metric from The Green Grid: annual site water use in liters divided by IT equipment energy in kilowatt-hours (L/kWh). Lower values mean less water per unit of computing.

Do closed-loop data centers use water?

Very little for cooling once filled, because the same water recirculates. They still use water for humidification, people and occasional top-up, and they usually use more electricity than evaporative designs.

Is liquid cooling better for water use?

Direct-to-chip and immersion liquid cooling handle dense AI racks efficiently and, when paired with dry heat rejection rather than cooling towers, can nearly eliminate cooling-water consumption.

Which data center cooling method uses the least water?

Air-side economization in cool climates and closed-loop systems with dry coolers use the least on-site water. Evaporative cooling towers use the most.

HOW ARGOS HELPS

Phreatic — groundwater availability

Sustainable yield and drawdown forecasts for a site’s wellfield across its design life.

CARI — aquifer reasoning agent

Ask whether a site’s aquifer can support a facility’s peak water demand.

SOURCES

Figures are taken from the primary sources above and dated as of the update shown. Concentrations are expressed in mg/L. Spot an error? Email support@argostellus.com.

RELATED GUIDES

Need a site-specific answer?

Argos models groundwater availability, drawdown and contamination for individual sites and portfolios.

CONTACT ARGOS