STRAIGHT ANSWER
What is WUE (water usage effectiveness) and why is it not the whole story?
WUE is liters of site water used per kilowatt-hour of IT energy. It is an efficiency ratio, not a total. A large campus with a low WUE can still consume more water than a small campus with a high one, and the numerator may mean withdrawal or consumption depending on the company.
The context
Recent fleet WUE disclosures: Microsoft 0.27 L/kWh (FY2025, down from 2.3), Amazon 0.12 L/kWh (2025), Meta 0.19 L/kWh (2024). These use different boundaries and years and are not a ranking.
What this answer does not say
- That the company with the lowest WUE uses the least water.
- That WUE includes water used to generate electricity. It does not unless a source WUE is added.