Water Usage Effectiveness (WUE)
WUE is The Green Grid's companion metric to PUE, measuring annual site water consumption per kilowatt-hour of IT energy. It captures evaporative cooling and humidification draws that PUE ignores, and is increasingly tracked as data centers expand in arid regions.
**Water Usage Effectiveness (WUE)** is a sustainability metric for data centers introduced by The Green Grid in 2011 to complement Power Usage Effectiveness (PUE). It is defined as: WUE = Annual Site Water Use (litres) / IT Equipment Energy (kWh) WUE has been formalized as ISO/IEC 30134-9. The metric exists because PUE ignores water entirely: a facility can post an excellent PUE while consuming millions of litres per day in evaporative cooling towers, adiabatic coolers, or humidification systems. Two cooling architectures with the same PUE can have radically different water footprints depending on whether they reject heat by evaporation or by sensible-only air or refrigerant cycles. The Green Grid defines two variants. **Site WUE** counts water consumed at the facility itself. **Source WUE** adds the water used upstream to generate the electricity the data center draws, which can dominate the total when grid power comes from thermoelectric plants. Reported site WUE values range from below 0.1 L/kWh for dry-cooled facilities in temperate climates to over 2 L/kWh for evaporative designs in hot, dry regions. Water reporting has become a regulatory and reputational issue as hyperscale operators expand in drought-stressed regions. Some operators now publish WUE alongside PUE and have invested in air cooling, dry coolers, or reclaimed-water sourcing to reduce potable-water draw. WUE shares PUE's main blind spot: it does not measure the usefulness of the work performed by the IT load.