What are PUE and WUE in Data Centres?

13 July 2026

Every search and AI query you run has a physical footprint and it’s thirstier and hungrier than most people realise.

Behind the screen, data centres consume electricity to run servers and networking equipment and to keep from overheating. Additionally, cooling towers, evaporative systems and humidification units consume vast quantities of water to keep the digital world running smoothly.

As data centre capacity races to keep pace with demand, both energy and water performance are moving to the top of the list of priorities.

Two metrics are commonly used to assess these areas:

Power Usage Effectiveness: PUE
Water Usage Effectiveness: WUE

Direct Air Capture (DAC) can support both areas when it is integrated with the data centre’s waste heat and cooling systems as certain solid sorbent DAC systems can use low-temperature waste heat, recover water and provide data centre cooling.

What is PUE?

PUE stands for “Power Usage Effectiveness” and measures how much of a data centre’s total energy is used by its IT equipment.

Therefore, PUE is a metric showing energy efficiency in a data centre.

It is calculated as follows:

PUE = Total data centre energy use ÷ IT equipment energy use

IT energy includes the electricity supplied to:

Servers
Data storage
Network equipment

Total facility energy also includes supporting loads such as cooling equipment, uninterruptible power supplies and lighting.

PUE Calculation Example

Assume that a data centre uses 75 MW of electrical power. Of this, 50 MW is supplied to IT equipment.

PUE = 75 MW ÷ 50 MW

PUE = 1.50

A PUE of 1.00 would mean that all facility energy was being supplied directly to IT equipment. In practice, some supporting energy will always be required.

Therefore, a lower PUE normally indicates that less energy is being used for cooling, power conversion and other non-IT loads.

What Does PUE Include?

PUE normally includes energy used by:

Cooling systems
Pumps and fans
Electrical distribution equipment
Uninterruptible power supplies
Lighting and building services

Cooling can represent a large part of the non-IT load because heat generated by servers must be removed continuously.

What Does PUE Not Measure?

PUE does not measure the amount of useful computing work completed. A data centre with a low PUE could still use more electricity than necessary if servers are underused or inefficient. PUE also does not show the carbon intensity of the electricity supply.

Waste heat reuse is another limitation. Standard PUE does not provide a direct credit when data centre heat is exported or used by another process.

PUE should therefore be assessed alongside:

IT equipment utilisation
Carbon Usage Effectiveness (CUE)
Energy Reuse Effectiveness (ERE)

What is WUE?

WUE stands for “Water Usage Effectiveness” and measures the amount of water used by a data centre in relation to the energy consumed by its IT equipment.

Therefore, WUE is a metric showing how efficiently a data centre uses water.

It is calculated as follows:

WUE = Annual data centre water use in litres ÷ Annual IT energy use in kWh

WUE Calculation Example

Assume that a data centre consumes 10 million litres of water per year and that its IT equipment uses 8 million kWh per year.

WUE = 10,000,000 litres ÷ 8,000,000 kWh

WUE = 1.25 L/kWh

A lower WUE indicates that less water is being used relative to the data centre’s IT energy demand.

Where is Water Used in a Data Centre?

Water may be used for:

Cooling towers
Evaporative cooling
Humidification
Cleaning and general building use

Water-cooled systems can reduce cooling electricity demand but water may also be lost through evaporation and blowdown/bleed (draining water from the cooling system for maintenance). Dry cooling can reduce site water consumption, although more fan energy or a larger heat rejection system may be required under some conditions.

As a result, PUE and WUE should be assessed together. A design change that reduces water use could increase electricity use. Alternatively, evaporative cooling could improve PUE while increasing WUE.

How Can Direct Air Capture Be Integrated with a Data Centre?

Some solid sorbent Direct Air Capture systems (How does Direct Air Capture Work?) can be regenerated at temperatures below 100°C, such as NEG8 Carbon’s DAC technology. This creates an opportunity for low-temperature heat from data centre cooling systems to be used in the DAC regeneration process. Instead of rejecting all server heat to the atmosphere, part of the heat could be transferred to the DAC system.

A combined system could include:

Heat being collected from server or liquid-cooling circuits.
Heat being transferred to the DAC regeneration stage.
Concentrated CO₂ being produced for storage or use.
Cooler water being returned to the data centre for re-use.

This approach allows the data centre’s waste heat to become an input to another process.

For more details, see Sustainable Data Centres with Direct Air Capture

Can DAC Improve Data Centre PUE?

DAC can support lower facility energy demand when it is integrated with the cooling system, but a lower PUE is not automatic.

Reducing Cooling Demand

A DAC unit can act as a thermal load when data centre waste heat is used for sorbent regeneration. Heat is removed from the cooling loop and transferred into the DAC process. If this reduces the operating demand of chillers, cooling towers or dry coolers, the data centre’s non-IT electrical load falls.

Can DAC Provide Cooling for a Data Centre?

DAC is not treated as a replacement for the main data centre cooling system. Instead, cooling support can be provided by accepting heat from the data centre’s water or coolant circuit. The DAC system then functions as a secondary heat sink during sorbent regeneration. The cooled water can then be returned to the data centre and the heat extraction lowers the energy demand on conventional cooling systems.

For more details, see Data Centre Cooling Solutions with Direct Air Capture

Can DAC Improve Data Centre WUE?

If water recovered via the DAC process is fed back into the data centre it reduces the amount of mains water required. This works in the case of a DAC process that produces water as a by-product of CO₂ capture such as in NEG8 Carbon’s DAC system. Recovered water can be used as part of the data centre cooling-system although treatment may be required before the water can be used and the water quality checked.

Water production varies according to:

Sorbent chemistry
Ambient humidity
Regeneration method

Careful reporting would still be required and gross water use, recovered water and net external water demand should be reported separately.

Conclusion

PUE measures how much facility energy is required to support IT equipment while WUE measures how much water is used relative to IT energy demand.

Certain solid sorbent DAC technologies can support improvements in both areas when they are integrated with data centre infrastructure. However, the result depends on the DAC process, cooling design and local climate.

When designed as one thermal and water system, a data centre and DAC plant can reduce heat rejection demand, recover water and remove CO₂ from the atmosphere to help decarbonise data centres.

For more:

Interested in NEG8 Carbon’s CO₂ capture technology?

Contact the NEG8 Carbon Team