we already have heating plants that transfer heat to homes via water, couldnt they just do that instead of wasting all the drinking water?
this post was submitted on 11 May 2026
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I think it would be a huge infrastructure project. But yeah, makes way more sense logically. Although knowing these AI dip shits they'd probably charge you a ton even though you're basically using their "waste". Almost like "I know what I got" Facebook marketplace post.
Other commenters correctly describe the cost analysis for using evaporative cooling, but I'll add one more reason why it's the preferred method when water is available: evaporating water can dissipate truly outlandish amounts of heat with very few moving parts.
Harkening back to high school physics class, water -- like all other substances -- has a certain thermal capacity, meaning the energy needed to increase the temperature of 1 kg of water by 1 degree C. The specific thermal capacity of water is already quite high, at 4184 J/(kg*C), besting all the common metals and only losing to lithium, hydrogen, and ammonia. In nature, this means that large bodies of water are natural moderators of temperature, because water can absorb an entire day's worth of sunlight energy but not substantially change the water temperature.
But where water really trounces the competition is its "heat of vaporization". This is the extra energy needed for liquid water to become vapor; simply bringing water to 100 C is not sufficient to make it airborne. Water has a value of 2146 kJ/kg. Simplifying to where 1 kg of water is 1 liter of water, we can convert this unit into something more familiar: 0.596 kWh/L.
What these two physical properties of water tell us is that if our city water comes out of the pipe at 20 C, then to get it to 100 C to boil, we need the difference (80) times the thermal capacity (4184 J/kg*C), which is 334,720 J/kg . Using the same simplification from earlier, that comes out to be 0.093 kWh/L. And then to actual make the boiling liquid become a vapor (so that it'll float away), we then need 0.596 kWh/L on top of that.
Let that sink in for a moment: the energy to turn water into vapor (0.596 kWh/L) is six times higher than the energy (0.093 kWh/L) to raise liquid water from 20 C to 100 C. That's truly incredible, for a non-toxic, life-compatible substance that we can (but should we?) safely dump into the environment. If you total the two values, one liter of water can dissipate 0.69 kWh of energy per liter. Nice!
In the context of a 100 megawatt data center (which apparently is what the industry considers as the smallest "hyperscale data center"), if that facility used only evaporative cooling, the water requirement would be 144,927 L/hour. That is an Olympic-size swimming pool every 6.9 ~~seconds~~ hours. Not nice!
And AI datacenters are only getting larger, with some reaching into the low single-digits of gigawatts. But what is the alternative to cooling the more-modest data center from earlier? The reality is that the universe only provides for three forms of heat transfer: conduction, convection, and radiation. The heat from data centers cannot be concentrated into a laser and radiated into space, and we don't have some sort of underground granite mountain that the data centers can conduct their heat into. Convection is precisely the idea of storing the heat into a substance (eg water, air) and then jettisoning the substance.
So if we don't want to use water, then we have to use air. But for the two qualities of water that make it an excellent substance for evaporative cooling, air doesn't come close -- 1003 J/(kg*C) and no heat of vaporization, because air is already gaseous. That means we need to move ungodly amounts of air to dissipate 100 megawatts. But humanity has already invented the means to do this, by a clever structure that naturally encourages air to flow through it.
The only caveat is that the clever structure is a cooling tower, and is characteristic of nuclear power stations. It's also used for non-nuclear power station cooling, but it's most famous in the nuclear context, where generators are well into the gigawatt range. Should AI datacenters use nuclear-sized air cooling towers instead of water evaporation? It would work, but even as someone that's not anti-nuclear, the optics of raising a cooling tower in rural America just to cool a datacenter would be untenable. And that's probably why no AI datacenter has done that.
To be abundantly clear, I'd rather not have AI datacenters at all. But since the question was why water consumption is such a big deal, it might be best to say that it's a physics problem: there isn't any other readily-available way to provide cooling for 100+ megawatts, without building a 100+ meter tower. Water is always going to be cheaper and more on-hand than concrete.
Followup: what are the impediments to using, say, seawater instead?
People mentioned corrosion which is true of all sea water systems but in evaporative systems you also have the addition of salt forming on all the evaporative surfaces which can drastically increase corrosion more than normal seawater and cause fouling
So to do this properly you would want an RO system making freshwater before the cooler which at that point it would make more sense to just have a separate company doing desalination.
Salt water is a huge pain to work with. The salt would quickly corrode any cooling systems.
And even for fresh water, you have biofouling to worry about and what to do with the water after you've used it, can't just dump it into the environment untreated.
There are already heat exchanging systems that do this with brackish water already; you don't need to treat water if all you ate doing to the water is making the water hotter or colder.
While not strictly biofouling, the marine environment can definitely be affected by introducing hotter water where it didn't exist prior, in and around the outflow pipe. Seaside nuclear power stations that use seawater cooling need to be mindful to diffuse the heated water over a large area, to minimize the ecological impact. Citation: https://ui.adsabs.harvard.edu/abs/2025EcInd.17012986J/abstract
I agree that pumping in water at a different temperature can affect the environment. It is just that a lot of people tend to conflate the effluent coming from plants like this as something which needs chemical or other treatment when the issue is thermal only.
Very similar problems arise with desalination plants, which I wrote about here: https://sh.itjust.works/comment/14613302
Ok follow up question here. Is there cause to be concerned that releasing tons and tons of steam into the environment that was not there before will cause other environmental impact beyond just the reduced water supply? Like.... If the ambient air is cooling all that water back into rain or something will that tangibly impact temperatures, or will average humidity change? Or is that part at least too small of an impact to be particularly material?
Not meaningfully, no. In the middle of a dry desert far from other bodies of water you could theoretically form cumulus clouds downwind of your site (I have heard of this happening), but it would be teeny tiny.
The amount of water evaporation is just orders of magnitude too small. The earth gets about 1kW of energy per square meter, so a 9GW data center is approximately the same amount of waste heat as 9 million square meters, which is 900 hectares.
I doubt that it has meaningful impact on climate. Evaporation from plants and oceans is many orders of magnitude greater. The issue is pretty always about fresh water availability in the given region.
There is almost certainly an impact somewhere, but I don't have the data to know where it is. My conjecture is that a localized mass of steam would cause convection currents and drive microweather phenomena, especially downwind of such an air cooled facility. I'm not sure rain is necessarily the result, unless there's a sizable mountain downwind, since although hot air will rise, it might run out of steam (pun intended) before cooling down enough to fully condense out. So it might just be adding a layer of humidity that floats a few hundred meters above the surface.
But even that could be devastating, if said layer blocks natural convection currents over a downwind town or city. It could act as a thermal cap, making that town warmer at night, because heat rising from the city would meet that humid layer and get absorbed by the water. The thermal capacity of water comes into play again, but this time against the city.
Heat energy is a driver for cyclones, such as when the warm, moist water of the Caribbean accelerates air as it approaches the southern USA, and only once landborne does it start to slow down due to drag and losing its energy source. I doubt we'll ever have an AI-induced hurricane, but in a situation where there's already an energetic weather event, it cannot possibly help to be adding heat to that situation.
I defer to the meteorologists to say what happens to the local weather and climate, and biologists on what happens to humans and wildlife. But I can't see it being good, no.
if that facility used only evaporative cooling, the water requirement would be 144,927 L/hour. That is an Olympic-size swimming pool every 6.9 seconds. Not nice!
You mean 6.9 hours? You're definitely off by a few orders of magnitude there.
Darn, you're right, the hours fell off in my dimensional analysis. Corrected, although 6.9 hours for a pool isn't much time for swimming at all.
So is air cooling actually feasible but we don't do it cause it would make data centers look like nuclear reactors? Or is it just not feasible?
AFAIK it's feasible for most data centers except the where power density is so huge that you just can't do it with air cooling. That issue is most common for large scale AI data centers.
Modern CPU consumes ~150W, modern AI chip can eat 700W and they're packed as densely as possible with multiple cards slotted in every motherboard.
Air cooling is feasible, as evidenced by existing power stations that use air cooling. A lot of newer nuclear generation use water cooling, being sited along the ocean and in the multi gigawatt range. But we can also find examples of inland power stations that have no water connection, and therefore need some massive cooling towers. Here is one in Germany that has a 2.2 GW rating and a 200 meter tall tower: https://en.wikipedia.org/wiki/Niederaussem_Power_Station
This is, as you can imagine, rather expensive to build, but it's doable. Cooling a coal fire is not substantially different than cooling compute loads in a data center, as it's all just a matter of moving heat around. Will there be differences due to the base temperature of coal versus GPUs? Yes, since the ratio of input to ambient temperature matters. But on the flip side, this should make it easier to construct, as the plumbing for lower temperatures is simpler.
Mechanical engineers can chime in on feasibility for AI data centers, but seeing as it hasn't been done, it's probably still cost related.
It evaporates, that’s how it cools. The water is sprayed over a heat exchanger and gets turned to essentially steam and then new water is pumped in and thus the water is “gone”. It will fall as rain somewhere but likely not near where it was taken from.
A closed loop system could be used but they are more expensive and require more maintenance so large data centers don’t usually use them unless required to.
Every car in the world uses a closed loop cooling system that does not consume water.
You're almost right, but there do exist air cooled engines with no conventional radiator or water/antifreeze pump..
https://en.wikipedia.org/wiki/Volkswagen_air-cooled_engine
Many motorcycles also use air cooling.
Car cooling systems are stupidly expensive, run at temps that would damage computer CPUs, run outside, and have a really nice advantage over computers which is that at higher heat loads they also tend to go faster thus cooling them off faster.
Now imagine you redlined a dozen cars for days on end in a garage in the middle of the summer do you think you might damage some components?
It is still very possible to use closed loop cooling on data centers but any system you build needs to be able to work in summer temps which can be as high as 35-40C and needs to do that without letting the computers exceed 60C. An air cooled system to handle that much heat is going to be very expensive and use a ton of power (and power generation also uses water)
Ok so what you're telling me is power plants generate electricity by burning fossil fuels which power a turbine with steam, then the data center uses all that electricity to produce even more steam?
And all that is to... Produce steamy furry porn
The most funny thing is, that once trained, the model can run and make furry porn on your local machine. So they don't even make any money on this.
I haven't tried furry porn models in particular, but all local image generation I've tried locally was really bad. It was with a 3070, so nothing really meant for this.
Mainline stable diffusion is pretty horrible. Try using SDXL community fine tunes (if they fit into your VRAM). They're worse than cutting edge cloud models, but they punch way above their league
I have bad news for you; it's all steam. EVERYTHING is steam. 🌍🧑🚀🔫🧑🚀🌚
Even you and I are just steam in liquid and solid phases.
I am still learning. Thank you for your educational comment.
I loathe AI anyways, I just wanna better understand why I loathe AI...
Further to this, as well as the source of the water often being the local city's drinking water supply (as we've found this puts a strain on that supply), evaporative cooling systems concentrate the minerals / contaminants in the water, meaning a smaller (relative to what is evaporated) of now highly-concentrated runoff water also has to be constantly disposed of. This likely is also going into the city's wastewater systems.
Radiators for closed-loop systems do also occupy more space (for the same cooling capacity) versus evaporative cooling towers, and are more limited in the range of climates they can be deployed in.
On balance though, the closed-loop cooling should always be the first choice; if it works for the deployment it will never be the wrong choice on a long-term / total cost of ownership basis.
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more expensive
That's the real reason right there.
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The rate that water returns to aquifers it was drawn from is very slow. Rainfall from the evaporation is only the first step of a long process. So it's not contamination, just being used up faster than is reasonable.
I can't touch on all of them, but a lot of them do actually just make it disappear.
A lot of the large data centers use evaporative cooling. The water basically boils off as vapor they just pump into the sky. This is cheaper in many places than the electricity needed for condenser cooling or other methods as it requires less electricity. (Which at the scale of these data centers they literally are unable to get enough electricity). That water vapor can drift off as clouds and come down somewhere, but no guarantee where or when.
Some data centers also introduce more runoff of pollutants from their methane generators and such that can make the water unusable. If they do capture the vapor and reintroduce into the water table it isn't always cooled down and the heat can cause major problems in the environment by raising temperatures. This can sometimes lead to the only thing surviving around the data centers being toxic algae or something.
There are so many more ways they can be problematic. That's just scratching the surface
Can this steam be used to turn turbines to make power? Or is it not hot enough to generate the required pressure?
Surely it could at least be fed into a power station that now only needs half the fuel to get it up to temperature?
It's definitely not able to run a turbine as is but either way it doesn't really solve the problem. My understanding is steam turbines don't actually condense or cool the water all that much. You still have hot water, maybe not fully boiling but still hot enough you'll have a not insignificant amount of evaporation and environmental damage if you just dump it. There's condensing and non condensing designs but the condensing design requires massive cooking towers and more water draw from a heat exchanger.
I'm not a systems engineer so calculating potential cost savings of adding the remaining heat to capture power vs just letting it evaporate vs using a closed loop system is outside my wheelhouse.
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The water is used to absorb heat and reject it outside. It will not be contaminate. It evaporates into the air which depletes local water supply. Could it come back? Sure. Can you guarantee it will? No.
Agriculture by and large still uses the most water but in the year of our lord 2026 theres no reason to not be building closed loop data centers. Evaporative cooling is mostly done in places where water is cheaper than power. Its still grossly irresponsible but that doesnt matter if their arent laws on the books.
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This is the sort of critical thinking that gets u in trouble with the hive mind. Yeah its water. About 2-5% of the water evaporates the rest is just some slightly warmer water.
Alright, so what do we do with that "slightly" (infact quite a bit) warmer water?
Can't just discharge it into a river. That hot water is gonna cause all kinds of havoc on the environment. Even if the temperature doesn't outright kill things, warm water holds less oxygen so that's going to harm fish, it's probably gonna fuck up their spawning cycles because suddenly they have warm water in the middle of winter, it might cause algae blooms, etc.
So we have to cool that water down. How are we gonna do that? We can spend even more money and energy to refrigerate it I suppose, but of course that would be stupid since these data centers are already using ridiculous amounts of energy.
So most likely we'd just put it in some giant holding tanks and wait for it to cool off or maybe run it through a massive radiator to cool off. That's even more land being taken up by these monstrosities, more maintenance needed, and at the end of the day, that's still water sitting around somewhere besides in our aquifers and waterways where it's needed, and we're probably going to be losing even more to evaporation in the process.
And while it's being pumped around in those data centers, I'll bet you it's being run though all kinds of plastic pipes and such, maybe coming into contact with lead solder and such because these aren't potable water systems, sounds like a great way to introduce more heavy metals and microplastics into the environment to me.
And that 2% or so that's being lost to evaporation? Some of these large data centers are using well in excess of a million gallons a day, so that's 20,000 gallons a day lost to evaporation, so roughly every month you're losing an entire Olympic sized swimming pool to evaporation. Again, that's water that's supposed to be in rivers and aquifers that's now not.
And what doesn't evaporate? Well now any minerals, heavy metals, etc. that were in the water are now concentrated by that much. Hope your water treatment is prepared to handle that.
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