What is water usage effectiveness (WUE), and why are published figures not comparable?
Water usage effectiveness is the ratio of water used to IT energy consumed, expressed in litres per kilowatt hour. It is a useful internal efficiency metric and a poor comparison metric, because operators calculate it on different bases and rarely publish which basis they used.
The three choices that change the number are whether it counts withdrawal or consumption, whether it counts only cooling water or all site water, and whether it includes the water embedded in purchased electricity. Two facilities with identical physical water use can report figures that differ severalfold purely through these choices.
Published fleet averages illustrate the problem. Amazon reports 0.12 litres per kilowatt hour on a withdrawal basis. Microsoft reports 0.27. Those numbers cannot be placed side by side and read as better or worse, because they do not measure the same quantity.
WUE is also a fleet average, which means it says nothing about the basin a specific facility sits in. A low fleet WUE is compatible with a severe local impact during a drought month. This is why a seasonal, basin-specific operating envelope is more informative to a council than any efficiency ratio.
Sources
AWS reports 0.12 L/kWh and Microsoft 0.27 L/kWh; the bases differ and the figures are not directly comparable
Company sustainability reporting, 2025ISO 30134-9, the WUE standard, is under revision
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