How do I calculate WUE for a data centre or server room?

Divide the site's annual water use in litres by the IT equipment's annual energy in kWh. WUE = litres of water / IT kWh, reported in litres per kWh. Take water from the meters on cooling towers, evaporative coolers and humidifiers, and IT energy from the UPS output meter, over the same 12 months.

What goes in the water figure

• Make-up water to cooling towers, including what is lost to evaporation and blowdown.
• Water for evaporative or adiabatic coolers and humidifiers.
• Water treated on site for these uses, counted at the point it enters the system.
• Leave out kitchens and washrooms if they are metered separately, and say so. If they share a meter, state that the figure includes them.

What goes in the energy figure

The denominator is IT equipment energy, the same figure used for PUE: servers, storage and network gear, measured at the UPS output, the PDU output or the equipment itself. State where you measured it. Do not divide by total facility energy; that gives a different and smaller number.

Site WUE and the water behind your electricity

Site WUE counts only water used at your premises. An air-cooled server room with no evaporative cooling can show close to zero. The Green Grid also describes a source-based figure that adds the water used to generate your grid electricity. If you publish that one, name the water factor you used and keep it apart from site WUE.

Reading the result

• Compare against your own past years, not a published average from another climate.
• Raising chilled water or supply air temperature can cut both energy and water; switching from evaporative to air-cooled chillers cuts water and often raises PUE. Track WUE and PUE together.
• Report the measurement point, the 12 month period and what the water figure includes.

Illustrative example: one year for a server room with a cooling tower

• Cooling tower make-up meter: 540 kL = 540,000 litres
• Humidifier meter: 0 litres (none installed)
• IT energy at UPS output: 300,000 kWh
• WUE = 540,000 / 300,000 = 1.8 litres per kWh

Figures are illustrative, not a benchmark.

What Senseible does here

Senseible reads the site's electricity bills and applies 0.710 kg CO2 per kWh for the emissions side; the water and UPS meter readings for WUE come from your facility logs.

• PUE formula and what a good PUE is
• Cloud and data centre emissions calculator
• Water intensity for BRSR

Sources: ISO/IEC 30134-9, Data centres key performance indicators, Part 9: Water usage effectiveness (iso.org)

Last reviewed 2026-10-18. Check the current edition of ISO/IEC 30134-9 before citing it in a report.