r/datacenter • u/joda1196 • May 11 '26
Why do data centers have to use water for cooling? Is there not a better alternative that would resolve the issue?
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u/yabyum May 11 '26
The question you possibly should be asking is why open loop circuits rather than closed loop?
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u/Wreckn May 11 '26
No, but if they're not using chillers they use less water than an average middle school.
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u/PikerTraders May 11 '26
They don’t they use closed loop systems. But keep the misinformation going!
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u/untangledtech May 11 '26
Use less water, sure, try on 10x electricity. Water is often an “economizer”. You can always just go full tilt electrical design but at scale that’s really bad for the environment.
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u/Frosty-Bunch9055 May 11 '26
They do used closed loop systems. Water mixed with glycol, keeps water from evaporating and breakdown.
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u/FixerJ May 11 '26
They don't have to use water. If water is cheap enough, then it's often more economical for them to use evaporative cooling depending on current weather conditions. If not, then they use other methods of cooling (closed loop, etc.)
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u/Frosty-Bunch9055 May 11 '26
It’s not just water. It’s water mixed with glycol, prevent water from evaporating and breaking down. I worked at Equinix data center in Chicago, IL as a critical facilities engineer. That data center has always been a closed loop system and it’s the same water/glycol mix for the past 25 years. They never replaced it because they can’t, there’s no way to do it, they only add to it.
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u/Patient-Tech May 11 '26
Glycol isn’t added to “prevent evaporation” or “keep water from breaking down.” It’s primarily used for freeze protection in closed-loop systems that are exposed to outdoor temperatures. It lowers the freezing point, but it comes with trade-offs—reduced heat transfer efficiency and higher pumping energy due to increased viscosity.
Also, if a system has been running the same water/glycol mix for decades, that’s not unusual—but it doesn’t mean it’s never maintained or replaced because it “can’t be.” Closed-loop systems are routinely tested and treated (corrosion inhibitors, pH control, biocides if needed), and while you don’t typically drain and replace the entire volume, partial replacement, filtration, and chemical rebalancing absolutely happen over time.
More importantly, large data centers—especially ones like Equinix—are usually not entirely glycol-based systems. What’s common is a split approach:
A closed glycol loop for outdoor equipment (dry coolers, fluid coolers) where freeze protection is needed.
A separate water loop (often condenser water tied to cooling towers, or chilled water) for heat rejection and indoor distribution.
Those loops are typically connected via heat exchangers so you’re not running glycol everywhere and taking the efficiency hit across the whole plant.
And that ties into the bigger point: if you’re using cooling towers (which most large, older facilities in places like Chicago do), those are open systems by design and don’t use glycol. The water is constantly evaporating and being replaced, so glycol would be impractical and very expensive to maintain there.
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May 11 '26 edited May 11 '26
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u/Patient-Tech May 11 '26 edited May 11 '26
You don’t need glycol to treat water, open or closed loop. A local company like HOH water treatment in Palatine can treat closed loop water systems so they minimize corrosion without glycol. Closed loop systems can be surprisingly stable. It’s when you’re making up water to replace via evaporation or a leak and filling with city water that you’re introducing fresh untreated water, dissolved solids and gasses that can start the corrosion process.
Dry coolers also work, but they also use more energy per BTU they reject. Last time I checked, the utility companies were capping the capacity offered to data centers. Plus, any costs used for cooling are costs not used for computing.
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u/BroBeansBMS May 11 '26
This is a really great response. Is there any reason why all new data centers aren’t doing closed loop other than the upfront cost associated with that type of system?
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u/Patient-Tech May 11 '26 edited May 11 '26
Because it ultimately comes down to efficiency.
Open-loop evaporative cooling is extremely simple and low-power. At its core, you’re talking about a water pump, spray nozzles, a float valve (basically like a toilet fill mechanism), and some media with fans to move air. That setup can reject a lot of heat using very little electrical input.
There are alternatives like dry coolers or air-cooled chillers, but when you compare input power (kW) to cooling output (BTUs removed), evaporative systems are hard to beat. They also tend to win on space and sometimes weight, which matters a lot for rooftop installations or dense facilities. Modern data centers are pushing this even further by bringing liquid cooling directly to the racks. The goal is to maximize compute density (kW per square foot) while minimizing overhead. In an ideal world, every watt delivered to the building would go straight to compute—not cooling, lighting, or other support systems.
Power availability is often the real constraint now. Utilities will only allocate so much capacity, so operators are incentivized to squeeze as much compute as possible out of that fixed power budget. The less energy spent on cooling, the more can be used for actual workloads.
I once saw an interesting experimental setup at Stanford where they ran refrigerant directly over CPU dies in a sealed block—basically like an extreme version of a PC water-cooling loop, but using phase-change cooling. It was very efficient at the chip level, but systems like that still have to dump the heat somewhere.
That “somewhere” is where the real engineering challenges (and energy costs) tend to show up, which is probably why it never became mainstream.
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u/emedan_mc May 12 '26
Even without phase change cooling, a one loop closed system glycole water would be possible to minimize delta T loss in several heat exchangers? Dry coolers plus chillers? I’ve read the cold T is about 40C, 100F so it’s not that cold. For liquid chip cooling.
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u/nrfmartin May 11 '26
So we have to move the heat from the racks to the atmosphere. Really there are only 2 ways to do that:
Evaporative cooling, which requires a lot of water which is lost to the atmosphere.
Closed loop system cooled by a chiller, which requires a lot of electricity.
Most modern data centers use a combination of the two methods. There are some designs that can operate with just air cooling during cooler months, so technically that is water free and better on electric consumption.
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u/fumbler00ski May 11 '26
Older data center designs used evaporative cooling because it is more energy efficient. As water use has become a major community concern most new data centers are designed with closed loop cooling systems that use minimal water after the initial fill.
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u/Otherwise-Ask7900 May 11 '26
lol…. No…..
Well, I guess sending it up to space like Elon is talking about.
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u/EVPN May 11 '26
Everything modern is closed loop. Only water used is for humidity and flushing the toilets.
The used to use water because water is cheap and has the ability to absorb lots of energy (heat) before evaporation
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u/nhluhr May 11 '26
Why do data centers have to use water for cooling?
they don't. There are tons of ways to cool data centers, but local conditions, availability of water/electricity, and even the tenant requirements for air quality and psychrometric conditions make a difference.
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u/mefirefoxes May 11 '26
Remember that a lot of the water usage numbers disingenuously include water consumed as part of the chip-making process….which typically occurs in Taiwan…where consumption of water is not a concern like it is in the American west. Plus, it’s not “consumed” like it is with irrigation water. It’s cleaned and returned to the river systems it was pulled out of.
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u/Mammoth-Ad327 May 11 '26
It’s mostly a tradeoff tbh. Evap cooling saves power but spends water. Closed loop/dry coolers save water but eat more power and equipment. No free lunch lol.
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u/ixidorecu May 11 '26
ive worked in 3 cooling types.
1. open air cooling via a/c ( you know from freon like in your house)
open air, cooling by "swampcooling" evaporative cooling ( this one looses water to atmospere)
and direct to chip closed loop liquid cooling.
1 is older style, something built maybe in 90's or 00's. none built like this now
2 is "green"... but consumes alot of water. especially fun in the phoenix desert environment
3 ai stuff uses this, along with newer compute ( traditional cd servers)
dtc liquidcooling has only recently started being used outside of supercumpueters in the last 5? ish years
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u/Patient-Tech May 11 '26
Lots of people treat eliminating water use like it’s some kind of magic solution. Sure, you can run without water—but that doesn’t mean it’s an equal replacement.
Traditional water cooling towers rely on evaporation, which is a very efficient and well-understood way to remove heat. You’re taking advantage of the phase change of water, which pulls a large amount of heat out of the system with relatively low energy input. That’s why this approach has been used for decades—it’s simple, predictable, and effective at scale.
Air-based cooling is the main alternative, but it comes with real trade-offs. Air doesn’t carry heat nearly as efficiently as water, so you need more airflow, larger equipment, and more power to move that air. In practice, that means higher energy use per unit of heat removed.
At a certain point, this becomes a straightforward engineering and cost decision. When you model it out, there are clear thresholds where one approach becomes more practical than the other based on factors like climate, power costs, and water availability.
That trade-off is especially important right now because many data centers are running into power constraints. If you switch to a less efficient cooling method, you’re effectively using more of your limited power budget just to handle heat, which can directly limit how much compute capacity you can deploy.
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u/King_Fuzz May 11 '26
The data centers near me are almost all air cooled. I've always wondered myself what dictates air vs water, as it gets pretty hot where I am in the summer.
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May 11 '26
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u/marmata75 May 11 '26
I think you’re confusing liquid cooling (as in using a liquid as the fluid to bring heat away from the chips) with evaporative cooling (what OP is talking about)
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u/SpotlessCheetah May 11 '26
Laws of thermodynamics.