Water: Cooling, Aquifers and Reclaimed Supply

Servers turn electricity into heat. Every kilowatt that goes in comes out as warmth that has to be carried away, and the cheapest way to carry heat in most climates is to evaporate water. So data center water use is mostly a cooling choice. The same building can use a lot of water or almost none, depending on design, climate and what the operator decided to trade off.

How cooling works

Method	How it works	Water on site	Electricity
Evaporative (cooling towers, adiabatic coolers)	Water evaporates and carries heat away. Some water is also flushed to control mineral buildup.	High	Lower
Closed-loop with dry coolers or chillers	Coolant circulates in sealed pipes. Fans and refrigeration reject heat to the air.	Low after initial fill	Higher, worst on hot days
Outside-air economizer	Filtered outdoor air cools the room when it is cool enough outside.	Low (sometimes misting on hot days)	Low in cool climates

Most real sites mix these. A campus may run on outside air in winter and switch to evaporative assist in July. Meta told the public its Kuna, Idaho data center would average about 70,000 gallons a day, roughly 80 percent below industry norms, mostly by using winter air cooling, according to the Idaho Conservation League. That is an average. The July number will be higher.

Liquid cooling for AI chips, where coolant runs to cold plates on the processors, is often described as water-saving. Inside the building it is a closed loop. But the heat still has to leave the building, and the final step can be a cooling tower or a dry cooler. Ask about that last step.

The national numbers

LBNL's 2024 report estimated US data centers directly consumed about 17 billion gallons of water in 2023, as reported by the Conversation and Latitude Media. It also estimated a much larger indirect footprint, around 211 billion gallons, from water evaporated at the power plants that supplied the electricity. Direct use could double or quadruple by 2028 under its scenarios.

For scale: 17 billion gallons a year is about 47 million gallons a day across the whole country. A single mid-size city can use that. The national total is not huge. The local total can be, which is why the whole debate is about specific aquifers and specific water systems.

WUE and the gallons math

Water usage effectiveness is liters of site water divided by kilowatt-hours of IT energy. Reported figures cover a wide range, as of October 2026:

• Industry average often cited: about 1.8 L/kWh (TechTarget, July 2025, which gives no underlying source).
• AWS fleet claim: 0.15 L/kWh.
• Microsoft global average: 0.30 L/kWh, down from 0.49 in 2021.
• Microsoft Arizona sites: 1.52 L/kWh.

Company fleet averages blend cool and hot sites. Do not apply a fleet number to a desert site.

Real reported examples

Site or company	Reported water	Note
Google, Council Bluffs, Iowa (2024)	about 1 billion gallons	Google's highest site that year
Google, Storey County, Nevada (2024)	about 1.5 million gallons	Air-cooled
Google, Pflugerville, Texas (2024)	about 10,000 gallons	Air-cooled
Google, all operations (2023)	6.4 billion gallons, about 95% at data centers	Company report
Meta, all operations (2023)	813 million gallons, about 95% at data centers	Company report
Meta, Kuna, Idaho	about 70,000 gallons a day, average (projected)	Company figure via ICL
Microsoft, Mt. Pleasant, Wisconsin	about 350,000 gallons on peak day (projected)	Closed-loop design; TechTarget figure, no source given

Amazon's sustainability reports do not disclose how much water the company uses (it publishes the fleet WUE above instead), and Microsoft reports operations as a whole rather than data centers separately, according to the University of Wisconsin-Milwaukee researchers Peyton McCauley and Melissa Scanlan. Disclosure is voluntary in most states. That gap is worth pressing on: ask the company and the local water provider for site-level numbers.

Virginia's JLARC found in 2024 that most data centers there use about as much water as a large office building or less, while a few use a great deal more. An October 2026 opinion piece in Cardinal News by independent researcher Tommy Turner reported that a Virginia DEQ simulation of a 3-million-gallon-a-day withdrawal for an evaporative hyperscale campus failed permitting criteria at all nine coastal plain locations tested. His link for that goes to his own site, not a DEQ document, so ask DEQ for the simulation before you repeat it. Both findings can hold at once. Averages are modest; the outliers are what break aquifers.

Idaho's 2026 cooling-water law

In 2026 the Idaho Legislature passed House Bill 895, which added Idaho Code 42-252. Data centers, as the tax code defines them, that begin construction on or after July 1, 2026 may not use water for cooling as a consumptive use unless the water comes from a municipal, water district, or water and sewer district system. The bill's findings tell the director of the Department of Water Resources to treat data center water use as conflicting with the local public interest when weighing permits and transfers. For a new Idaho project, that means a well and a water right purchase no longer settle the cooling question; the water has to come through a public system, and the course on Data Center Planning Issues follows what that does to siting.

Aquifers, peaks and reclaimed water

A March 2026 paper by Yuelin Han, Pengfei Li, Adam Wierman and Shaolei Ren argues that peak-day demand is the real constraint on public water systems. Cities size wells, treatment plants and pipes for the hottest day, which is also when evaporative cooling peaks. Their estimate: at 2024 water intensity, US data centers could need 697 to 1,451 million gallons a day of new water capacity through 2030, roughly New York City's average daily supply. If water intensity instead falls 10 percent a year, their range drops to 227 to 604 million gallons a day. They also note the trade-off: water limits push operators toward dry cooling, which raises electricity demand on summer peaks.

In much of the West, groundwater is governed by water rights and the prior appropriation doctrine. A new user needs a right, a transfer or a contract with a city that has one. Ask which.

Reclaimed water is the usual answer to "you will drain our wells." Tucson's Project Blue proposal, tied to Amazon Web Services and developed by Beale Infrastructure, planned to use drinking water for at least two years and then switch to reclaimed water once a new line was built. The Tucson City Council rejected the annexation and water deal unanimously in August 2025. The developer returned with a design that cools with electricity, needing 287 MW from Tucson Electric Power by 2028, according to KJZZ. Water fight became power fight.

In Idaho, the unpassed 2026 House Bill 609 would have required future recipients of the data center sales tax break to notify the local water provider in writing before construction began. It shows how lawmakers have tried to tie incentives to water disclosure.