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Comment by MeteorMarc | Hacker News Reader

And all these huge new data centers are gonna make things worse: https://www.eesi.org/articles/view/data-centers-and-water-co...

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The idea that data centers are huge water hogs is nonsense.

Data centers consume enormous amounts of water for evaporative cooling. What part is nonsense?

If the data center is built somewhere with ample water supplies this isn't an issue. If it's pulling from groundwater this can be a huge issue. Groundwater isn't infinite and is being depleted in many areas.

They’ll be built and deployed in space soon. Elon said so.

The reason they consume water is the same reason space is a bad place to put data centres, getting rid of the heat is a challenge. Having only radiative heat dissipation is going to severely limit space based manufacture and computing, it puts significant constraints on the space station already.

yeah but Elon said so and thus it must be true

I was under the impression they capture the evaporation, let it cool, and recycle it?

I guess it's possible to have a condensing station, but generally speaking you'd need to supply input energy to allow it to cool down and condense somehow. The bigger question here is if a datacenter using evaporative cooling where does the moisture go? If it just feeds a cloud system that rains on nearby fields, it's not much different than irrigating crops. If it feeds clouds that go offshore and rain into the ocean, it's similar to just diverting drinking water into the ocean

I must be missing something, why can't it be entirely closed loop like a water radiator in an old car? A simple fan running through large radiator cores would certainly condense within the system, keeping the water in the system

A closed loop system has a COP of 4, adding in cooling towers almost doubles that to 7. You can reject 1.75x more heat for the same amount of electricity by adding evaporative cooling towers.

COP is coefficient of performance.

One thing to remember is that much of the waste heat from your car's engine goes out the exhaust, not out the radiator. I think the two are often about equal.

A 1 GW heat source evaporates about 9 million gallons per day.

In 2024, US data centers consumed power at an average rate of about 21 GW.

So, that would be about 70 billion gallons per year evaporated.

> I was under the impression they capture the evaporation, let it cool, and recycle it?

So, how do they get rid of the latent heat of evaporation that's released when the water recondenses?

The whole point of evaporative cooling is to soak up that latent heat and release it later, out in the environment, when the water recondenses somewhere else.

It's kind of like why Dune's stillsuits don't work.

In the USA, data centres consume about 164 billion gallons of water annually [1]

Irrigation consumes 118 billion gallons per day [1] and thermoelectric power plants a further 133 billion gallons per day.

There's enormous amounts, and there's enormous amounts. If you really want to get mad about water being wasted, look up what californian alfalfa growers pay for their water.

[1] https://www.eesi.org/articles/view/data-centers-and-water-co... [2] https://pubs.usgs.gov/fs/2018/3035/fs20183035.pdf

New datacenter projects are usually closed loop now.

From your first citation:

> Closed-loop cooling systems enable the reuse of both recycled wastewater and freshwater, allowing water supplies to be used multiple times. A cooling tower can use external air to cool the heated water, allowing it to return to its original temperature. These systems can reduce freshwater use by up to 70%.

Citation please, I don’t buy it. Evaporative cooling towers almost double the efficiency of heat rejection vs a closed loop system. I don’t see any data center operator giving up those operating cost efficiency gains just to save some water, but I could be wrong.

As i stated, It's literally in the first link from the OP.

Yeah, I still don’t buy it. No data center operator is going to use almost twice as much electricity to operate their cooling system if they could install evaporative cooling towers and almost double the efficiency of heat rejection. You can remove 7W of heat for 1W of electricity with a cooling tower, it’s 4W for 1W with a closed loop system. I could see them doing it in a humid area where you can barely get any cooling from evaporation due to the air being satured, but that only covers the Deep South and Florida in the US.

I don’t care if some company operating data centers claim that they’re aiming for closed loop cooling systems when the economics favor open loop cooling. Show me the incentive and I’ll show you the outcome, the incentive to increase profit by using cooling towers will beat out the abstract good feeling you get from not using evaporative cooling towers and paying almost twice as much to reject heat from your data center which you only operate to make a profit.

It's not a question of quantity but of distribution.

I'm not defending the waste of water that is growing alfalfa in the desert for export, but there are plenty of places datacenters are built where the water they use is impactful.

They can both be bad. Unlike the legal mess that is US irrigation water rights, data centers are also a lot easier to do something about.

Most new datacenters use closed loop systems now. the water just circulates.

The water used by data centers are either closed loop, meaning that they recirculate a set amount of water.. or the water evaporates, and my understandingis they don't use potable water for those systems. I might be wrong, but I don't think data centers aren't destroying potable water.

The water is reutilized, a big reason is the difficuty to filter new incoming water because of impurities and uncertainty about quality (e.g. winter times make the river water very muddy and difficult to filter).

Second because is because adding water is a cost, whereas reuse existing water is simpler and saves money. There are always losses of water, however these are neglectible.

Not mentioned here but for more extreme cases of devices cooling is done with distilled water (zero minerals) and the whole device works submerged under this water, the hot water isn't thrown away because it distilled water takes a lot of effort to remove the minerals and effort to keep them out, so the closed loop is very efficient.

Here's one in Oregon from today's San Francisco newspaper. If they recycle, it's still loses enough equivalent to 4000 people a year. Maybe that's worth it, but it reads like it's not enough for their future plans. It's not like the city population in question has changed that much historically so there's some future expansion of something planned. That water sounds very pristine since they are going to have to take over national park land. https://www.sfgate.com/national-parks/article/mount-hood-wat...

Microsoft is piloting new zero water cooled datacenters in some locations https://www.axios.com/local/des-moines/2026/01/16/microsoft-...?

Hopefully this can be the new standard.

yes, yes, AI bad.

https://substackcdn.com/image/fetch/$s_!Dy-x!,w_1272,c_limit...

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