What is WUE?

WUE (Water Usage Effectiveness) is a sustainability metric for data centers that indicates the efficiency of water usage. More precisely, the figure relates the annual water consumption in liters to the total power of all active IT components in kilowatt-hours. Thus, Water Usage Effectiveness indicates how much water a data center actually consumes per unit of IT performance provided.

The Formula

Formula: WUE = Water quantity / IT Equipment Energy

Interpretation

A low WUE value means that a data center consumes little water per unit of IT performance generated. The ideal value is zero: it is achievable if there is no continuous water extraction from surface or groundwater, but rather the data center’s cooling is achieved through a closed cooling system without evaporation. The industry average is approximately 1.8 l/kWh; data centers with evaporative cooling can reach values up to 2.5 l/kWh.

WUE and PUE: A Conflict of Objectives

WUE (Water Usage Effectiveness) and PUE (Power Usage Effectiveness) are partially contradictory and should not be considered in isolation. Evaporative cooling improves PUE because less electricity is needed for cooling. At the same time, however, the required water significantly worsens the WUE value. A good PUE value therefore does not indicate whether energy efficiency is achieved at the expense of higher water consumption. Those who consider both metrics together get a more complete picture of a data center’s sustainability.

Why WUE is Becoming More Important

Water is an increasingly scarce resource; after the drought year 2018 and subsequent drought periods, this also applies to Germany and Europe. A data center can consume several dozen cubic meters of water daily. The WUE value is gaining importance as an ESG metric, but it should also not be neglected for operational reasons: data centers run around the clock and rely on continuous cooling. If water as a cooling medium becomes scarce (e.g., due to drought or official withdrawal bans), a failure is imminent in the worst case. Consistent optimization of WUE is therefore also a matter of operational safety.

WUE of FRA7

For the new FRA7 data center in Rosbach, which is under construction as of August 2026, firstcolo is planning a closed liquid cooling circuit without evaporation and without water extraction from or discharge into water bodies. This is expected to achieve a WUE of approximately 0 l/kWh for technical cooling.