Water usage effectiveness, or WUE, is the main number data centers use to report how much water they use. It is simple on paper, and it hides a few things worth knowing before you compare one site to another.
The WUE formula
WUE is the water a site uses in a year, in liters, divided by the energy used by its IT equipment in kilowatt hours. If a site uses 100,000 liters and its IT gear uses 50,000 kWh, the WUE is 2.0 liters per kWh. The Green Grid introduced the metric in 2011 as a companion to PUE, according to industry trade coverage.
A real company number
Microsoft reports a fleet WUE of 0.30 liters per kWh for fiscal 2024, down from 0.49 in 2021. That is a company reported figure, and it is a good example of how the metric is used to show progress over time.
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What WUE leaves out
Researchers note several limits. WUE counts water used on site, not the water used to make the electricity. It is a ratio, so a big site with a good ratio can still use a lot of water in total. Figures can be counted as water consumed or water withdrawn, and the two are not comparable. The common protocols also do not separate reclaimed water from drinking water.
Why the numbers are patchy
A study of the top 20 operators found 13 report both PUE and WUE, while 7 do not report WUE publicly. Meters matter too, since a whole building meter can pick up landscaping and restrooms.
What this means for operators and neighbors
If you run a site, report WUE every year with the method stated, and publish total water use next to it. If you live near a project, ask the operator for the annual figure and the source of the water. Those two requests turn a marketing number into something a community can check.
Water is local. A good ratio in a wet region and the same ratio in a dry one are not the same story, so context belongs in every report.
How to read it
Ask three things when you see a WUE number: is it consumption or withdrawal, what year does it cover, and where does the water come from. A low WUE is a good sign, but the full picture also needs total water use and local supply.
Every figure in this article comes from the sources listed below, and where a number is company reported we say so. Our Eco Tools page has a water estimator that gives a quick sense of scale for a data center. If you spot a mistake, tell us and we will fix it.
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Submit your companySources: Data Center Knowledge WUE guide; Koomey review of top 20 operators; Microsoft datacenter cooling. Figures marked as company reported come from the company itself.
