Data Center Water Requirements and Cooling Choices

Most data center water use is for heat rejection. Servers turn nearly all the electricity they use into heat, and that heat has to leave the building. Evaporating water is a very efficient way to move heat, which is why evaporative systems are common. The water that evaporates is consumed and does not return to the source.

Other uses are smaller but still need planning:

• Cooling tower blowdown: water drained to keep dissolved minerals from building up, which becomes wastewater.
• Humidification and adiabatic assist on air handlers or dry coolers during hot periods.
• Domestic water for staff, plus landscaping where it is used.
• Fire protection: sprinkler supply and, often, on-site storage tanks and pumps sized to the fire code and the local fire authority.
• Make-up water for closed loops, which is small once the loop is filled.

There is also an indirect water footprint in the power supply, since many power plants use water for cooling. That does not show up on the site’s water bill, but it is part of the full picture.

The cooling design is usually set by the developer or end user, but the site influences it. A site with abundant water and a mild climate supports different choices than a hot, dry site with tight water supply.

The tradeoff is real. Choosing a dry design to save water raises energy use and can raise the peak power the site has to request from the utility. Climate decides how big that penalty is, which our guide to climate and cooling in site selection covers.

Water Usage Effectiveness (WUE), defined by The Green Grid, divides a facility’s annual site water use in liters by the energy used by its IT equipment in kilowatt-hours. Lower is better. The Green Grid also describes a source-based version that adds the water used to generate the facility’s electricity.

WUE is useful for comparing designs, but it is an annual average. For site selection, the more important figure is often peak daily demand on the hottest days, because that is what the water supplier and the wastewater system have to handle. Ask the design team for both the annual volume and the peak day.

WUE and PUE (Power Usage Effectiveness) usually pull in opposite directions. A design that improves one tends to worsen the other, so look at them together.

Municipal or regional water utility

The simplest source when capacity exists. Confirm treatment and supply capacity, the size and pressure of the nearest main, any required extensions, connection fees, rate structure and drought curtailment rules. A written capacity or will-serve statement from the utility is a useful early step.

Groundwater

On-site wells can work where aquifers are productive, but they need hydrogeologic testing and, in most states, permits. In much of the western U.S., water law follows prior appropriation, where rights are based on seniority of use. Many eastern states follow riparian principles with state permitting overlays. Rules vary widely by state, and some areas restrict new large withdrawals.

Reclaimed water

Treated wastewater from a municipal plant can supply cooling towers and reduces demand on drinking water supplies. It requires a pipeline from the treatment plant, an agreement with the operator and treatment suited to its quality. Proximity to a wastewater plant is worth noting in screening.

Surface water

Rivers and lakes can supply large volumes, but withdrawals usually need state permits or water rights, and intake structures can trigger federal review under the Clean Water Act.

Evaporative cooling concentrates the minerals in the water, and the system has to bleed some of it off as blowdown. That wastewater needs a destination. Discharging to the municipal sewer requires capacity at the treatment plant and often an industrial user permit with limits on what the water can contain. A direct discharge to a stream needs a National Pollutant Discharge Elimination System (NPDES) permit under the Clean Water Act.

Some sites treat and reuse blowdown on site or move toward zero liquid discharge, which reduces the burden on local systems but adds equipment and cost. Stormwater is handled separately, through site grading, detention and stormwater permits.

Water use is one of the most common local concerns about data centers, particularly in areas with drought history or stressed aquifers. Projects that use low-water cooling, reclaimed water or a clear drought operating plan tend to have an easier conversation. Our guide to community engagement covers how to address these concerns early and accurately.

When we screen a site, water review starts with the cooling assumption, because a dry-cooled campus and an evaporative campus have very different needs. Then:

• Identify the water provider and request capacity, main size and pressure at the site.
• Check groundwater conditions, state permitting and any local restrictions on new wells.
• Locate the nearest wastewater treatment plant and ask about capacity for blowdown and reclaimed water availability.
• Review drought history and the provider’s curtailment rules.
• Confirm fire flow and whether on-site storage will be needed.
• Note the local attitude toward water use, from public records and prior projects.

Water is one line in the full site selection checklist, and it is rarely evaluated in isolation from power and climate.