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

Canonical: https://senseible.earth/answers/data-centre-wue-water-usage-effectiveness

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](https://senseible.earth/answers/pue-formula-and-good-pue)
- [Cloud and data centre emissions calculator](https://senseible.earth/calculators/cloud-data-centre-emissions)
- [Water intensity for BRSR](https://senseible.earth/answers/water-intensity-calculation-for-brsr)

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

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