WUE (Water Usage Effectiveness) Explained with a Calculation
PUE tells you how much power the facility wastes; WUE tells you how much water it uses. Here is the formula, a worked example, and what moves the number.
The formula
WUE = annual site water usage (litres) ÷ annual IT equipment energy (kWh).
Worked example
Assumptions (illustrative): 1.2 MW average IT load running all year, and 20,000 m³ of site water use per year.
- IT energy = 1,200 kW × 8,760 h = 10,512,000 kWh
- Water = 20,000 m³ × 1,000 L/m³ = 20,000,000 L
- WUE = 20,000,000 ÷ 10,512,000 = 1.90 L/kWh
The efficiency calculator covers PUE, WUE and CUE.
What moves WUE
- Heat rejection method: cooling towers consume water by evaporation; air-cooled plant uses little.
- Climate and humidity, which set how much evaporative cooling is available.
- Water treatment and blowdown practice.
- IT load: the same water use over a lower IT energy gives a higher WUE.
The PUE trade-off
A design can improve PUE by using evaporative cooling and worsen WUE in the process. Judge them together and against local water availability. See PUE explained and chilled-water vs air-cooled.
Written by the Vision Matrix Institute editorial team. Worked examples use stated, illustrative assumptions; check them against your project data, the applicable standards and manufacturer datasheets before use.
Frequently Asked Questions
What is WUE in a data center?
Water usage effectiveness is the annual site water consumption divided by the annual IT equipment energy, expressed in litres per kilowatt-hour (L/kWh).
What is a good WUE?
There is no single target; it depends on climate, cooling technology and water source. Lower is better, and a design with no on-site water use for cooling can have a very low value, though it may use more electricity.
How does WUE relate to PUE?
They often trade off. Evaporative and water-cooled designs can reduce energy use (better PUE) at the cost of water use (higher WUE), while air-cooled designs can do the reverse.
Does WUE include water used at the power plant?
The basic site WUE counts only water used on site. Some variants also count water used in generating the electricity; check which one a figure refers to.
Want to learn this properly?
This topic is covered in depth in our Electrical Design – Data Center Specialist program.
Ask us on WhatsAppLearn to do this on a full project in the Electrical Design – Data Center Specialist program, or read the data center design guide.