How Data Centers Use Water for Cooling

This guide explains how data centers use water for cooling, from the intake and treatment to the final destination of the water, whether it’s evaporated, recycled, or discharged. You’ll learn the key steps in both open-loop and closed-loop systems, what happens to the water after it absorbs heat, and how facilities manage water responsibly.

What You’ll Need

• Basic understanding of how a data center operates (servers generate heat)
• No special tools—just curiosity about industrial cooling systems

Step-by-Step

1. Understand the two main cooling types. Data centers use either open-loop (once-through or evaporative) or closed-loop (chilled water with cooling towers) systems. In open-loop, water is used once and then discharged or evaporated. In closed-loop, the same water circulates repeatedly, losing heat via cooling towers.
2. Water intake. Water is drawn from a municipal supply, well, lake, river, or ocean. The source depends on location and permits. The water is metered and may be treated with chemicals to prevent corrosion, scaling, and biological growth before entering the cooling system.
3. Heat absorption from servers. Inside the data center, water flows through pipes to cooling coils or rear-door heat exchangers. Warm air from servers passes over the cold coils, transferring heat to the water. The water temperature rises by 10–20°F (5–11°C) as it leaves the coil.
4. Transport to cooling equipment. The now-warm water is pumped to the cooling plant, which may be on the roof, in a basement, or in an adjacent building. In a chilled-water system, the warm water goes to a chiller (refrigeration unit) that removes heat, and the cooled water returns to the data hall.
5. Heat rejection in cooling towers (evaporative cooling). In most large facilities, the chiller’s condenser loop sends heat to a cooling tower. The tower sprays water over fill material while fans pull air through it. A small portion of the water evaporates, which removes heat from the remaining water. The cooled water returns to the condenser loop.
6. Water loss and makeup. Evaporation is the primary water loss. Additionally, some water is lost as drift (tiny droplets carried out with the air) and as blowdown—water deliberately drained to remove concentrated minerals and impurities. Makeup water is added to replace these losses.
7. Where the water goes after cooling.
   • Evaporated water becomes water vapor and goes into the atmosphere—it doesn’t return to the ground.
   • Blowdown water is discharged to the sewer or a treatment facility, or sometimes reused for irrigation or other non-potable purposes.
   • In once-through systems, the entire water volume is returned to the source (e.g., river or ocean) at a higher temperature, which can affect aquatic life if not managed.
8. Closed-loop systems with dry coolers. Some modern facilities use closed-loop systems with dry coolers (radiators) that don’t evaporate water. In these, the water never leaves the pipe; it’s cooled by air fans. This uses minimal water, but is less efficient in hot climates.
9. Water treatment and recycling. Many data centers treat blowdown water on-site (e.g., reverse osmosis) to reuse it. Others partner with local utilities to use treated wastewater (effluent) for cooling, reducing demand on potable water.
10. Monitoring and optimization. Facilities track water usage effectiveness (WUE) to measure water consumption per kilowatt-hour of IT energy. They adjust cycles of concentration, fan speeds, and schedules to minimize water use while maintaining efficiency.

Common Mistakes

• Assuming all data centers use the same cooling method—some use air cooling only, others use water.
• Confusing water consumption (evaporated) with water withdrawal (total taken). Consumption is what’s lost.
• Thinking that water in a closed loop is “used upâ€�—it’s not; it circulates, but evaporation still occurs in cooling towers.
• Ignoring the energy-water tradeoff: using less water often increases electricity use, and vice versa.

Tips

• Look for data centers that use recycled water or are located in cooler climates to reduce water impact.
• Check a company’s sustainability report—many publish WUE figures.
• Understand that water use varies by season and weather; more evaporation happens in hot, dry conditions.

Troubleshooting

• If water consumption seems too high: Check for leaks in the system, increase cycles of concentration (but watch for scaling), or adjust cooling tower fan speed to match load.
• If cooling towers are not cooling effectively: Ensure fill material is clean, water distribution is even, and fans are working. Also check for scale buildup.
• If you see white deposits around towers: That’s scale from hard water—improve water treatment or increase blowdown.
• If water temperature is too high: Verify chiller setpoints, increase water flow, or reduce server load.

Frequently Asked Questions

Q: How much water does a typical data center use per day?
A: A large data center can use millions of gallons per day, but average is about 3–5 million gallons per day for a 100 MW facility. Smaller centers use much less.

Q: Is data center water cooling bad for the environment?
A: It depends. Evaporative cooling consumes water, which can strain local supplies. However, many facilities use recycled water or dry cooling to minimize impact.

Q: Can data centers use seawater for cooling?
A: Yes, some coastal facilities use seawater once-through cooling, but it requires extensive filtration and anti-corrosion measures to protect equipment.

Q: What is water usage effectiveness (WUE)?
A: WUE is a metric that measures how many liters of water are used per kilowatt-hour of IT energy. Lower is better.

Q: Does water cooling make servers more efficient?
A: Yes, liquid cooling is more efficient at removing heat than air, allowing for higher-density servers and reducing fan energy.

Q: What happens to the warm water discharged from once-through systems?
A: It returns to the source, but the temperature rise can harm aquatic life. Regulations often limit the allowable temperature increase.

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