{"id":611,"date":"2026-07-03T17:11:30","date_gmt":"2026-07-03T17:11:30","guid":{"rendered":"https:\/\/rpmwes.com\/blog\/?p=611"},"modified":"2026-07-03T17:11:44","modified_gmt":"2026-07-03T17:11:44","slug":"data-center-cooling-water","status":"publish","type":"post","link":"https:\/\/rpmwes.com\/blog\/data-center-cooling-water\/","title":{"rendered":"Data Center Cooling Water: Where Millions of Gallons Go"},"content":{"rendered":"

Quick Answer<\/strong><\/p>\n

A large data center can consume millions of gallons of cooling water per day — up to 5 million gallons for the biggest facilities, according to the Environmental and Energy Study Institute’s 2025 analysis. Most of it leaves through the cooling tower: roughly 1.8 gallons evaporate for every ton-hour of cooling, per the EPA WaterSense mechanical systems guide (2017). The remainder exits as blowdown (concentrated water drained to the sewer) and a small amount of drift. At typical operating conditions of 4 cycles of concentration, about 75% of the water a cooling tower takes in evaporates and never reaches the sewer. Yet most utilities bill sewer charges on the full incoming meter reading — which is why evaporative-cooled data centers routinely accumulate sewer overpayments they can recover through evaporation credits.<\/p>\n

Why Cooling Dominates a Data Center’s Water Bill<\/h2>\n

Every kilowatt-hour a server draws becomes heat, and that heat has to go somewhere. In most climates, rejecting it with evaporating water is the most energy-efficient option available, which is why large data centers are plumbed more like industrial process plants than office buildings.<\/p>\n

The volumes add up quickly. The Uptime Institute (2016) estimated that a 1-megawatt data center using traditional chiller and cooling tower systems consumes about 6.75 million gallons of water per year, circulating roughly 855 gallons of condenser water per minute through its cooling tower.<\/p>\n

Scale that to a multi-building campus and you get the national picture: US data centers directly consumed about 66 billion liters (roughly 17 billion gallons) of water in 2023, with hyperscale and colocation facilities accounting for 84% of the total, according to Lawrence Berkeley National Laboratory’s 2024 United States Data Center Energy Usage Report<\/a>. For the full facility-level and national numbers, see our pillar guide to how much water a data center uses<\/a>.<\/p>\n

The 4 Main Cooling Technologies and Their Water Profiles<\/h2>\n

Not every data center drinks at the same rate. Water use depends almost entirely on how the facility rejects heat, and the 4 dominant approaches sit at very different points on the water-energy tradeoff.<\/p>\n

Water-Cooled Chillers With Cooling Towers<\/h3>\n

The workhorse of large facilities. Chillers move heat from the data hall into a condenser water loop, and cooling towers reject that heat by evaporating water into the atmosphere. This is the thirstiest design — Google reported that its average data center consumed approximately 450,000 gallons of water per day in 2021 — but also among the most energy-efficient: Google’s 2022 analysis found water-cooled data centers use about 10% less energy than many air-cooled equivalents.<\/p>\n

Air-Cooled Systems<\/h3>\n

Air-cooled chillers and dry coolers reject heat with fans instead of evaporation, consuming near-zero water on site. The tradeoff is energy: more fan power and higher condensing temperatures. Google’s 2025 Environmental Report describes choosing air cooling at new sites in Waltham Cross (UK), Mesa (Arizona), and Canelones (Uruguay) specifically because its water risk framework flagged those watersheds as high risk.<\/p>\n

Evaporative and Adiabatic Cooling<\/h3>\n

Direct and indirect evaporative systems cool air by evaporating water across media or spray, skipping the chiller entirely for much of the year. They can use less water than a chiller-plus-tower plant and far less energy, but consumption is seasonal — it spikes during the hottest weeks, exactly when local water systems are most stressed.<\/p>\n

Direct Liquid and Immersion Cooling<\/h3>\n

Cold plates and immersion tanks move heat from the chip into a closed liquid loop. The loop itself consumes no water; what matters is how heat leaves the building. Paired with dry coolers, site water use approaches zero: Microsoft’s next-generation design announced in December 2024 uses chip-level liquid cooling with closed-loop heat rejection and consumes zero water for cooling, avoiding the need for more than 125 million liters per year per data center, according to Microsoft.<\/p>\n\n\n\n\n\n\n\n\n
Cooling technology<\/th>\nSite water use<\/th>\nEnergy tradeoff<\/th>\nWhere the water goes<\/th>\n<\/tr>\n<\/thead>\n
Chillers + cooling towers<\/td>\nHigh (millions of gal\/year per MW)<\/td>\nMost efficient in most climates<\/td>\nMostly evaporation; blowdown to sewer; minor drift<\/td>\n<\/tr>\n
Air-cooled \/ dry coolers<\/td>\nNear zero<\/td>\nWater-cooled designs use about 10% less energy (Google, 2022)<\/td>\nNo site water; shifts water burden to power plants<\/td>\n<\/tr>\n
Evaporative \/ adiabatic<\/td>\nLow to moderate, seasonal<\/td>\nVery low energy use<\/td>\nEvaporation, with periodic flush\/blowdown<\/td>\n<\/tr>\n
Direct liquid \/ immersion<\/td>\nDepends on heat rejection; can be zero<\/td>\nSupports high-density AI racks<\/td>\nClosed loop; perimeter dry coolers or towers<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Evaporation, Blowdown, and Drift: Where the Gallons Actually Go<\/h2>\n

For the cooling tower systems that dominate the industry, every gallon of makeup water leaves one of 4 ways. The EPA WaterSense Water Efficiency Management Guide (2017)<\/a> states it as an equation: makeup = evaporation + blowdown + drift + leaks.<\/p>\n

Evaporation<\/strong> does the actual cooling. Regardless of tower efficiency, approximately 1.8 gallons evaporate for every ton-hour of cooling delivered, per the same EPA guide. This water leaves as vapor — it never touches a drain.<\/p>\n

Blowdown<\/strong> is the portion deliberately drained to the sewer to control dissolved solids. As water evaporates, minerals stay behind and concentrate; blowdown bleeds off the concentrated water before it causes scale and corrosion. We cover the mechanics in our guide to cooling tower blowdown<\/a>.<\/p>\n

Drift<\/strong> is mist physically carried out of the tower by the fan. Uncontrolled, it can run 0.05% to 0.2% of the recirculating flow, but modern drift eliminators cut it below 0.005%, according to EPA WaterSense (2017). Leaks and overflows should be zero in a well-run plant.<\/p>\n

Cycles of Concentration: The Dial That Sets Your Blowdown<\/h2>\n

Cycles of concentration (COC) is the ratio of dissolved solids in the tower water to dissolved solids in the makeup water — effectively, how many times each gallon is reused before being drained. It is the single biggest lever on blowdown volume. The Department of Energy’s Federal Energy Management Program<\/a> notes that many systems operate at 2 to 4 cycles, while 6 or more may be possible; raising cycles from 3 to 6 cuts makeup water by 20% and blowdown by 50%.<\/p>\n

Here is the math for a 1 MW IT load, using stated assumptions. At roughly 3.5 kW per ton, 1 MW of heat is about 285 tons of cooling. Running around the clock, that is 285 × 8,760 = about 2.5 million ton-hours per year. At the EPA’s 1.8 gallons per ton-hour, evaporation is about 4.5 million gallons per year.<\/p>\n

Blowdown then follows from cycles: blowdown = evaporation ÷ (COC − 1). At 4 cycles, that is 4.5 million ÷ 3 = 1.5 million gallons, for total makeup of about 6 million gallons — of which 75% evaporated. At 3 cycles the evaporated share is 67%; at 6 cycles it climbs to 83%. Our explainer on cycles of concentration<\/a> walks through the chemistry limits.<\/p>\n

Consumed vs. Withdrawn: Why the Difference Matters<\/h2>\n

Water accounting hinges on one distinction. Withdrawal is what you take from the supply; consumption is the share permanently removed from the local water cycle. LBNL’s 2024 report defines consumption as withdrawn water that is “permanently removed from the immediate water cycle” through evaporation or other irreversible processes. Google’s 2025 Environmental Report applies the same logic to its own accounting: consumption equals withdrawal minus discharge.<\/p>\n

For an evaporative-cooled data center, the two numbers are far apart. The facility above withdrew 6 million gallons but consumed 4.5 million; only the 1.5 million gallons of blowdown ever returned to the sewer. Efficiency metrics like water usage effectiveness (WUE)<\/a> are built on exactly this consumption measurement.<\/p>\n

What Evaporation Means for Your Sewer Bill<\/h2>\n

Here is the part most facility teams miss: the majority of commercial water utilities calculate sewer charges from the incoming water meter, on the assumption that what comes in goes back down the drain. For a data center evaporating 75% or more of its cooling water, that assumption fails by millions of gallons a year — and sewer rates are frequently half or more of a combined water\/sewer bill.<\/p>\n

The fix is documentation, not renegotiation. By submetering cooling tower makeup and blowdown, a facility can prove how much water never reached the sewer and apply for evaporation credits on its sewer bill<\/a>. Most utilities have an established process for this; our submetering and sewer credits guide<\/a> explains how the meters, math, and utility approval fit together. RPM Water Equity Solutions manages this process with nearly 200 utilities across 36 states.<\/p>\n

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Ready to Find Out What You Could Save?<\/h3>\n

Data centers with evaporative cooling often pay sewer charges on millions of gallons that leave as vapor and never reach the sewer. If your facility runs cooling towers, those overpayments are documentable — and recoverable.<\/p>\n

Request your free assessment today<\/a><\/strong> and find out how much you could recover.<\/p>\n<\/div>\n<\/div>\n

The Bottom Line<\/h2>\n

Cooling water will keep flowing as long as servers keep computing, and AI growth means the gallons are trending up, not down — LBNL projects hyperscale facilities alone could consume 60 to 124 billion liters annually by 2028. Operators who understand where each gallon goes — evaporation, blowdown, or drift — are the ones positioned to cut both consumption and cost. Metering that split is the first step, and it pays for itself on the sewer line of the very next bill.<\/p>\n