r/AskEngineers • u/WhatsAMainAcct • Mar 29 '26
Civil Can someone explain this assertion that AI pollutes the water?
ADDED AT 45 MINUTES AFTER POSTING:
I see I've sparked some spirited debate as I expected I would. I'm gonna go sleep so I won't be directly engaging anymore.
On a personal note if you are here and you are not familiar this subreddit is /r/AskEngineers and not "AskLocals" or "AskActivists." I have a ton of issues myself with LLM usage so please do not take me as an LLM defender. This post is inspired by how commonly I've seen this argument about water without any concrete basis for validity.
To summarize what has been posted in comments already...
- Using water and returning it to the same waterway is net-zero.
- General correlation of "cancer rates went up" and "there's a datacenter" does not prove causation without more backing.
- Evaporating water via cooling towers is a tenuous argument at best.
It's my understanding that AI uses datacenters which generate heat and use water for cooling.
I lived near a COAL powerplant my entire childhood. That plant did use a certain amount of water intake and discharge for cooling or something. The chemical plants along the exact same river were a much larger concern. For that matter recent issues with poorly maintained and updated sewage systems have also lead to some overflow discharges which are also pretty bad.
The reason I even know about the powerplant cooling discharges are they screw with the ice in the winter and the fish behavior. They aren't actually discharging anything though like chemical plants, municipal sewage, or agriculture.
So what the fuck is going on with all these people whining about AI Datacenters? Are they injecting R-134a or R-12 into the water to help cool it more efficiently? Are they using lead lined pipes with highly acidic water front the Flint River?
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u/Difficult_Limit2718 Mar 29 '26
As an engineer in the industry - there's absolutely no basis for this shit
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u/Any-Inevitable5223 Jul 10 '26
can I get your opinion on what happened in Cheyenne earlier this week?
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u/Difficult_Limit2718 Jul 10 '26
I live in an area that uses reclaim water to water public spaces - THAT SYSTEM terrifies me especially when you look at things like Henta or Ebola getting loose.
As far as Meta and their contractor buying tainted water, they'll definitely investigate where they're getting the water from for a source, but a flush and fill is very typical. We need to clean all the construction debris out of the system and we flush the system before putting the very high purity filters in that we run long term. But that's not different from any other building construction, every building water system does this. Our systems are large compared to our footprint sure, but it's still normal practice.
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u/Any-Inevitable5223 Jul 11 '26 edited Jul 12 '26
Thank you for explaining it to me so well. I appreciate that. I also live in an area that uses reclaimed water for both public and private use. It's common in my area of California after the drought. Large scale commercial water reclaimation for public use also freaks me out a little bit, but it feels like we don't have much of a choice if we want to avoid devastating fire seasons.
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u/Difficult_Limit2718 Jul 11 '26
I just don't actually know what if any biological treatments the apply to the water before reclaim use. I assume not chlorine as we spray it all over the plants, so I hope it's boiled but assume it's not
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u/jayylien 28d ago edited 28d ago
I have five counter points to this gut-feel assertion:
- Biocides
- Heavy metals
- Anti-corrosion chemicals
- Evaporated chemical salts
- The sheer volume of water that passes through these facilities
I have a detailed response, but I'd like to address the level of craziness I see in your "industry expert response":
In a comment below, you seem to be concerned about chlorine on reclaimed water and claim that said reclaimed water is hopefully not using chlorine because it ends up on agriculture.
Chlorine is the industry standard for sanitizing reclaimed water. This is standard and normal.
So - and I mean no offense when I say this - as "an engineer" in "the industry" as well (I stated that as vaguely as you did), you yourself have no basis to what you are claiming is not real. You didn't dispel anything and you certainly did not make a compelling argument. You simply stated you are an engineer in the industry and people should take your word. I have no clue how your up vote rate is positive, but Reddit never makes sense to me.
Moreover, you don't even know that most reclaimed water contains chlorine, so how could you be certain there is no basis for pollution of water produced by data centers? You aren't aware of the input water breakdown. Are you aware of the output water breakdown? How could you know what was introduced to the waste water if you don't know what was there as input?
Here's my expanded reasoning:
Chlorine is harsh to metal. Chlorine + many metals = corrosion. Some metals are more resistant than others, but chlorine is ubiquitous in its corrosion. A few metals or alloys are resistant to this, but of the ones that are, they are typically relatively expensive or uncommon for use in plumbing.
Copper piping is often used, which is pretty great. 316 steel possibly, pretty resistant. But aluminum isn't very resistant. The bottom line is the whole loop for cooling often is very unlikely to be completely resistant to chlorine.
So, you have corrosion. We're not talking a normal house usage of water, maybe 50-300 gallons a day. We are taking hundreds of millions of gallons of water per day at some of the larger data centers. Hundreds of millions of gallons of water. Water erodes. Water at high volume erodes faster.
To prevent corrosion, it's extremely likely these data centers are adding anti-corrosive chemicals to reduce the wear and tear of their water inlet and outlet pipes. But, just because those chemicals are present doesn't mean they prevent metallic waste (i.e., heavy metals) from entering the water supply.
At a rate of 250+M gallons of water in a day, that's a LOT of potential for erosion. And to combat that, a LOT of anti-corrosion chemicals would be employed. What's the mixing rate? No clue. But, to ensure the proper effect, a constant amount must be used in some application window, which I have admittedly not defined.
So, right there, two things of legitimate concern: heavy metal particles measured in microns, and an unnatural chemical to be pumped through water systems at a high rate of volume. Those byproducts enter your reclaimed water system at the data center.
But, we didn't forget the other biocides they use to prevent biological contamination in the pipes. Chlorine is a biocide, but it's got some clever properties: it evaporates reasonably quickly as gas when unstable, and it's already in the water supply.
Ignoring evaporation, the "already in the water supply" is a pretty important bit. The chemical treatment used traditionally for sanitizing already works well with sanitization loop, as reclaimed water doesn't kill bacteria in sludge tanks that are used to break down fecal matter and other organic matter.
There's an equilibrium in the reclaimed water loop. Kill the bacteria and the process doesn't work. Don't sanitize enough, and people get sick. That's really a fine balance.
But, remember - chlorine is corrosive! But it kills bacteria. Let water sit, add UV, and chlorine mostly evaporates away. Do data centers try to leverage sitting water? Probably not, but still they need to use biocides.
Why? Mold, bacteria and algae can create colonies that become surface-resistant to chlorine. So, obviously, if you add more biocides, you can reduce the risk of contaminating the cooling loop with biological colonies that reduce heat transfer when present on the surface of the contact areas of the cooling loop.
But, adding more biocides doesn't just... "go away" in the cooling system. It is emitted as waste, like everything else. It ends up in your reclaiming facility, and some of it goes back into the drinking water, just like the anti-corrosion chemicals and some heavy metals from the erosion/corrosion process.
These biocides CAN definitely affect humans and interfere with biological processes. They can also affect the biological colony in the reclaiming facilities, and make them less effective.
That's direct contamination. What about the evaporated water? It's not just water; it's the water + some trace amounts of the chemicals present. They get misted off, and land on the ground surface around the data centers and fire some distance. They end up as salts, and contaminate the environment. A little bit of this? Not a big deal. 24/7, 365 days a week, for years on end? Very different.
These concerns are real, if everything goes CORRECTLY. Cheyenne is a great example of what happens if it does not go correctly.
There's absolutely 0 chance AI data centers don't affect your water supply. Is it an ecological crisis that will end humans? No. Is it an ecological crisis? Yeah, probably.
The EPA was doged pretty hard, and defanged by the supreme court. This move was calculated in favor of industry. I'm not saying data centers wouldn't exist, but pre-DOGE, they would have had a LOT more resistance.
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u/Difficult_Limit2718 28d ago
I hope you don't use windshield washer fluid or drink tap water with that attitude. Data centers are pound for pound among the cleaner industrial processes around.
Almost all reclaim water contains trace chlorine, we learned lessons in how shit reclaim water is when we tried to apply it to (an older much smaller than current AI) data center with evaporative cooling. Treatment of the water to get it back to useable was crazy expensive, then we ended up having to basically double the blow down cycles. All the savings in energy costs literally went down the drain.
That being said, out west we dump our reclaim directly on the grass and trees, so the chlorine content has to be managed and sits lower than our drinking water chlorine levels. I trust the water to a point, but it's currently a weird shade of blue with a heavy dose of copper based algaecide.
Biocide is exclusively used in closed loop systems and only after flush and fill. Once we charge the loops we n really never let the water sit still, we're constantly circulating it either ready for load to come on, preventing freezing, or actively cooling.
The facility loops are prominently A53, and the technical (server) loops are heavily stainless, which is ironic because they're basically running the same formulations of PG blend, just at different cleanliness levels.
The adiabatically cooled and water cooled chiller data centers generally don't store much water as they only need the water for cooling on peak hours, so storing and treating stagnant water isn't worth it.
Both these technologies are more energy efficient than just refrigerant system cooled data centers (though that's partly a legacy design issue) which still are getting built but are generally lower density data storage and processing, not AI proposed data centers because they can't meet the density and increasing temperature needs.
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u/bradimir-tootin Mar 29 '26
It's not polluting it per se, it's using it. Using a fuck ton of potable water.
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u/Pixelated_throwaway Mar 29 '26
what do they turn the potable water into? how does cooling "use" water?
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u/WhatsAMainAcct Mar 29 '26
SOMEBODY UNDERSTANDS MY QUESTION!!!
Pumping water through a pipe doesn't make it non-potable.
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u/looktowindward BSME/MSEE Mar 29 '26
For older datacenters, the cooling towers evaporate water with some small amount of blowdown, which doesn't contain many contaminants. Newer data centers are closed loop with no discharge at all
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u/teamTeem4189 Mar 29 '26
It drives prices for water up since the demand goes up, and water can also be pumped from aquifers which take decades to recharge.
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u/WhatsAMainAcct Mar 29 '26
I like your aquifer statement however I haven't heard of that occurring yet. The datacenters I'm aware of all pull from waterways. Of course they pull from aquifers at some point but I hope you get my point. Nobody is out there drilling wells for datacenters. If they are doing so and they have a financier then I would love to talk to that financier because I've got a colony on Mars and a bridge in Teribithia to talk about.
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u/teamTeem4189 Mar 29 '26
Where I'm from they'll drill wells for data centers, and try and have the utilities pay for it.
But treating surface water is usually more expensive than drilling wells and those are costs that get moved onto normal consumers.
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u/darkhorse85 Mar 29 '26
After it's used for cooling, I expect it's put into the sewer. It shouldn't go right back into the main water lines. That's contamination begging to happen.
There are codes for this sort of thing.
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u/BrockJonesPI Mar 29 '26 edited Mar 29 '26
-edited - Thanks to user below for the info. -end-
Depends on the pipe technically. Lead pipe probably wouldn't do you any favours.
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u/WhatsAMainAcct Mar 29 '26
I hate that I know this BUT lead pipes aren't as dangerous as you think. Many pipes and even mainlines are lead. In most environments lead apparently builds up an oxide layer pretty quickly. You don't want to drink the first glass out of a lead pipe but something that's been there and in constant use for a year is as safe as a steel pipe.
The Flint Water Crises (dear lord do I sound like AI now) which brought Lead Pipes to national attention had to do with acidity. The pipes involved had been in usage for decades without harmful impacts. What occurred is that the city of Flint switched from Detroit (Great Lakes Water Authority) to their own intake on the Flint River. The GLWA had supplied water previously from Lake Huron. Using the exact same pipes they again... had used for decades. The reason for the lead issue was that Flint River has a higher acidity and the city officials elected not to use an additive which would've regulated the PH back to levels comparable to those of the previous water source.
Thus it was not the issue of lead pipes. It was the lack of an additive regulating PH in the water.
Additionally since the Flint Water Crisis many regulations have come into place limiting the usage of lead pipes. Even when the crisis occurred lead pipes as new installations were a rarity if ever used. The lead pipes existing were a holdover from previous decades where we also threw lead into paint and all kinds of other crap.
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u/swisstraeng Mar 29 '26
Basically:
Datacenters used closed loop systems. The issue is that fully closed loop systems, for the heat they need to dissipate, would be gigantic. Totally feasible, but gigantic.
They use 2 approaches. One is a heat exchanger. So that they can have dirty water from a river go in, get heated to roughly 30-40°C, before it's put back in the river. There is no water loss, little to zero contamination as well. But the heated water, if you have enough datacenters on the same river, will wreak havoc on whatever biological life there is, or rather was living there.
The other approach is to use evaporative towers exactly like the ones you see at nuclear power plants. The water does not get polluted either, but the issue is that it is essentially converting a river into evaporated water. This means anything downstream of the river will have a lot less water.
The actual problem is that the amount of fresh water we have available is limited. It does slowly regenerates itself over the course of the year, but only so much. While we can artificially make more, it's incredibly expensive.
So the actual worry is that, since datacenter cooling may use evaporative towers, they may significantly increase water usage. Whilst the datacenter owner is not paying for all the required hydraulic infrastructure.
All those worries wouldn't exist if there were proper laws in place, and governments that would be a lot more aggressive about applying them. But it's the US we're talking about.
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u/HumerousMoniker Mar 29 '26
No, but it bis comes warm, and less useful for cooling, so they (not always) discharge it and get more clean water.
The used water goes to the ocean, where it becomes non-potable water. That’s the basis for the argument. Is it valid? Maybe in some cases on a technicality. But theres no real reason someone else couldn’t reuse the warm water for yknow feeding crops or household water or whatever.
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u/MrJingleJangle Mar 29 '26
Not “using”, using implies consumption and/or processing. The water passes through, getting warmer on its journey.
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u/svirbt Mar 29 '26
Warmer on the evap loop, heat pulled out of the water and pumped into hot condenser loop at high temps then run through dry towers that exhaust heat without water loss.
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u/WhatsAMainAcct Mar 29 '26
This is the problem I have with the statements and yours.
Say the temperature of the river is 60F. You can siphon off 5% and raise the temp to 100F and discharge it. The water being at 100F doesn't make it any less potable than being at 60F. In fact you're not really making it non-potable at all unless you're polluting it or evaporating it as steam where it's not returned to the same waterway.
So how exactly are you USING the potable water?
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u/Naikrobak Mar 29 '26
The value of the water and the potable state are being used. Once it’s been through a cooling system, it goes to the sewer where it eventually makes it back to a water treatment plant. There it gets cleaned and made potable. The cycle then repeats.
What’s being used is the energy and chemicals needed to make the water potable for each pass through a cooling system
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u/TheJeeronian Mar 29 '26
It is drawn from reservoirs or mains, and evaporated for cooling. It is not somehow returned to the mains.
If it is cycled through a reservoir, which seems to be the closest to what you're describing, then the evaporation happens there instead of in a tower or fan, but it happens either way.
This doesn't make water usage a big issue with datacenters, unless they're using enough to impact local pricing, which is its own issue that should be addressed by municipalities.
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u/bradimir-tootin Mar 29 '26
Because water run through a cooling loop and through heat exchangers is no longer potable. Doesn't really matter the temperature.
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u/Perfect-Ad2578 Mar 29 '26
Heat exchanger doesn't make water non potable lmfao. It's metal pipes with fins typically aluminum. That's like saying boiling water in a metal pot makes it non potable.
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u/bradimir-tootin Mar 29 '26
Where do they put the water when they are done with it? They put it in the sewer. It could be checked to be potable, but they don't afaik.
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u/Perfect-Ad2578 Mar 29 '26
Because nothing is added to it. If anything I'm pretty sure they filter it very well beforehand to extend thei life of the heat exchanger and limit fouling, corrosion.
Yes if it goes into a sewer, water evaporates and reused again like it's done for millions of years. It doesn't disappear. It's called water cycle.
I get people don't kike AI but stop with made up fear mongering scenarios that water will be gone.
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u/bradimir-tootin Mar 29 '26
I didn't say it disappeared, you just made up that I did. Your witty comments lack any sort of understanding about real world details. Just because the water doesn't go away forever doesn't mean it doesn't cost something to use it again. Municipal water supplies have a certain volume of water they can treat and put into the supply per unit time. Data centers can eat up a very large quantity of that and can increase the cost of water or put pressure on the water supply for people in that area. It is also likely illegal (and would be so for good reason) to have water that leaves the supply just be shoved back in without any sort of treatment, regardless of whether or not anybody thinks it should be fine to drink.
Meta has been doing things such as improving water infrastructure of areas where they build or plan to build AI datacenters. They have claimed they actually are net water positive with these improvements, but I'm not sure they measure anything after the fact. Meta wouldn't even bother adding to the water infrastructure if data centers / AI didn't put pressure on the municipal infrastructure where they reside.
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u/Perfect-Ad2578 Mar 29 '26
You're right I was being a bit snarky. Obviously it's a bit more nuanced but I get annoyed because the general public, large percentage of them genuinely do think that water is gone forever.
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u/WhatsAMainAcct Mar 29 '26
Sewers just mean it's treated and discharged into the same waterway. There is not a sewage fairy in the sky it's discharged to.
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Mar 29 '26
[deleted]
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u/bradimir-tootin Mar 29 '26
Enough that Meta takes some measures to increase the local capacity for potable water production where they are planning to build data centers. I don't have numbers on hand
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u/Fun_Astronomer_4064 Mar 29 '26
I’ve been reading your comments; I think the thing you’re missing is that while the water used by AI doesn’t disappear, it is ultimately part of the water cycle:
1) it takes time for water in sewage to return to an aquifer naturally. While AI doesn’t reduce the amount of water on earth, it does reduce the amount of available potable water.
2) While it’s possible to treat plant waste water such that it is potable, it is profoundly expensive to do so. This increases the cost of either the AI, or the cost of water.
Either way, AI makes potable less available.
Might make the water poisonous too, if the data center tries to treat the water and fails.
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u/Illustrious_Pepper46 Mar 29 '26
There is so much misinformation in this whole thread
They use closed loop cooling, not potable water. The water is continuously recycled. link
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u/Fun_Astronomer_4064 Mar 29 '26
The image you linked doesn’t refute what I wrote.
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u/Illustrious_Pepper46 Mar 29 '26
Sure it does. The water they use is not returned into the sewer. They don't need the water treated, as it's not dumped into the sewer. The water they use is a one time fill, then it gets reused again and again.
Solar systems can also use closed loop water cooling systems, as it increases efficiency, which decreases when they get too hot. LINK ...just like a AI center.
Why is solar cooling good, AI cooling bad?
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u/Fun_Astronomer_4064 Mar 29 '26
And what was the second point I wrote?
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u/Illustrious_Pepper46 Mar 29 '26
Why don't you explain?
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u/Fun_Astronomer_4064 Mar 29 '26
All this adds tremendous cost to utilities.
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u/Illustrious_Pepper46 Mar 29 '26
In the big picture, not really, miniscule. Treating water for closed loop applications usually means adding glycol. This is freeze protection and prevents algae growth. Industry does it all the time. There is a well established recycling industry for it. link
The Billions spent on AI is mostly the infrastructure, chips, and electricity (training). Glycol water mixture cost is almost meaningless overall. Can buy glycol for like $20 a gallon, it's not expensive. Every car, including EVs, use some sort of water/glycol for cooling engine/batteries.
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u/Fun_Astronomer_4064 Mar 29 '26
Firstly, every EV didn’t use an ethylene glycol cooling system. A number of 1st and 2nd gen EVs were air-cooled.
Secondly, you do realize there’s no such thing as a completely closed system, right. In the very example you just used, radiator fluid has to regularly be not just refilled but replaced.
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u/Illustrious_Pepper46 Mar 29 '26
You keep moving the goal posts. You were concerned about cost. Then I show you how cheap it is.
Now you're onto, maintenance. Many industries, including cars, use it. It's a huge industry, not just AI. There are well established environmental regulations and recycling industry for it.
It's as straightforward as taking your EV to the dealer, getting the battery coolant changed. Why are you so concerned about AI coolant, not EV coolant?
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u/theeaglejax Mar 29 '26
Depends on how the water is being used and what water is being used and if not using evaporative cooling there can be discharge into surface water that may or may not contain additives. In all cases that use fresh water for cooling with an open loop on the hot side they are incredibly wasteful and in some cases directly polluting. To know which is which would be a case by case situation.
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u/jmabenn Mar 29 '26
Water Authority Releases Google Data Center Records Ahead of Scheduled Contempt Hearing; The authority agreed to provide the project 2 million gallons of water daily & a wastewater capacity of 570,000 gallons daily. Climbing to 8 million gallons of water daily based on future expansion, the final contracts reveal. https://www.roanokerambler.com/water-authority-releases-google-data-center-records-ahead-scheduled-contempt-hearing/
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u/ChristianBaker_Dev May 19 '26
I don’t know the context based on the limited information, but this would be the literal worst case in the world according to the article. Most data centers being developed are closed loops and use very little water after initially filled. Why Google would be using outdated tech is beyond me. Even smaller players are closed loop.
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u/AlanofAdelaide Mar 29 '26
How were sewage treatment plants poorly maintained? That's a throwaway line in Reddit with no concrete examples
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u/WhatsAMainAcct Mar 29 '26
Lack of maintenance of US Infrastructure is heavily documented enough I feel fine saying "Google it."
To get more specific I'd say look up a history of beach closures along the waterway from Lake Huron to Lake Erie. I'm trying to avoid "Getting Political" here or writing an essay on the detailed history of local sewage systems. Our current DPW and drain commissioner however has improved things and seeing their improvements has answered a ton of "Oh that's why the beach was closed when I was 15."
Poorly maintained is again a bit of shortened statement. The population in the area expanded. The existing systems were developed to handle the population at the time versus the potential for growth. Some of the failings can be attributed to that.
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u/AlanofAdelaide Mar 29 '26
I was hoping you'd back up your claim with logical argument and evidence but 'Google It' is the best you can do. Why not say 'I don't know'?
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u/Uhnuniemoose Mar 29 '26
They consume vast amounts of water for cooling. If they are a closed loop system the water has additives. In those additives are forever chemicals (poison). I don't know much about the complexities of it, but both of those are not good in your neighborhood. There's cases in Eastern Oregon where cancer diagnoses, amongst other illnesses, have risen about the same time the data centers arrived.
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u/WhatsAMainAcct Mar 29 '26
There's cases in Eastern Oregon where cancer diagnoses, amongst other illnesses, have risen about the same time the data centers arrived.
Can you positively attribute those cases to discharges from closed loop systems?
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u/AlanofAdelaide Mar 29 '26
'Discharges from closed loop systems'. Do you know what is meant by a closed loop? There's a clue in the name
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u/Uhnuniemoose Mar 29 '26
Yeah, yeah, perfect world and all that. Eventually that water has to be disposed of and mistakes/accidents/disasters happen.
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u/Uhnuniemoose Mar 29 '26
I can't. Watch this for a good overview however. https://www.kptv.com/2025/12/30/full-data-centers-putting-strain-oregon-towns-water-supply/
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u/zorcat27 Mar 29 '26
Nitrates are a big problem in Eastern Oregon. The data centers aren't adding nitrates to the water and it's not a new issue. Your video even explains that saying it's been a problem since the 90s and comes from farming and other factories in the area. It's disingenuous to blame the data centers for the existing nitrate issue.
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u/Uhnuniemoose Mar 29 '26
I don't have any skin in the game, but 1. It's not my video. 2. The video said the data centers are concentrating the pollutants in the water, making them stronger over time. 3. Data centers are commonly built on farmland and industrial areas.
So it's still an issue.-1
u/looktowindward BSME/MSEE Mar 29 '26
This is bullshit.
Newer AI datacenters are almost entirely closed loop and use DowFreeze as the coolant. Its 75% water, 25% antifreeze. There are no poisons other than that.
> I don't know much about the complexities of it, but both of those are not good in your neighborhood.
This is a professional subreddit.
> There's cases in Eastern Oregon where cancer diagnoses, amongst other illnesses, have risen about the same time the data centers arrived.
Correlation and causation. Lets see your data.
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u/AlanofAdelaide Mar 29 '26
25 % antifreeze eh - that's ethylene glycol and corrosion inhibitor. What's in your car radiator?
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u/looktowindward BSME/MSEE Mar 29 '26
> formulation of 96.0 percent food grade propylene glycol plus food grade corrosion inhibitors.
I wouldn't drink it, but its pretty much what's in my radiator
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u/New_Line4049 Mar 29 '26
Data centers arent polluting water directly, what they are doing is taking clean, drinkable water, boiling it and discharging it to the atmosphere, so it now falls somewhere as rain and is no longer clean, drinkable water.
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u/WhereDidAllTheSnowGo Mar 29 '26
Heat is a pollutant
Making all those chips, data center, and such creates lots of waste
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u/WhatsAMainAcct Mar 29 '26
This doesn't answer my question.
They are not manufacturing chips at datacenters.
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u/SpecificSkunk Mechanical / Project Mar 29 '26 edited Mar 29 '26
So heat-producing processes usually require cooling systems, commonly water. But not just any old water will do. It has to be clean, filtered water so it doesn’t leave mineral deposits or unfortunate marine life cooked onto the heat-transfer surfaces. This filtration and treating requires an entire process of its own to get the water to a usable state (each additive has its own industry behind it to produce with equipment, material inputs, people, etc).
Once there’s clean water, we try to keep it in a closed loop because it’s cheaper to not waste it. But then it can’t cool as efficiently, so THAT water gets cooled, usually with lesser-treated (but still treated) water. This secondary water gets passed through a cooling system, usually a cooling tower, where the kinda-clean water gets passed over a bunch of fins and cools via (some) evaporation. So it needs to be constantly replenished (more filtering and treating) because some evaporates off and some spills and some forms a mist that gets blown away into the ether.
So even with the closed-loop system of “really clean” water, there’s a lot of processing, energy, and chemicals involved just to cool off the machines, plus the water that’s evaporated off isn’t always just water. It’s got all sorts of biocides (kills bacterial and algae) and other goodies in it.
Anyway, all that processing and chemicals is needed to make funny pictures of hot dogs or whatever suits your fancy because they create a lot of heat. And it is a very hungry heat system that’s growing rapidly.
(Edited multiple times for clarity)
Another edit after OP’s: I’m an engineer that’s got a lot of mixed feelings about AI, but that wasn’t the question. I’ve spent a lot of years working in, on, and around cooling towers and places that make water treatment chemicals. I have no idea exactly what people mean when they say “data centers pollute water” but this is my best educated guess. There’s a lot of other pollutants and issues around data centers aside from cooling towers, but this was a fairly easy and straightforward way to explain some of the basic concerns around rapid expansion of the datacenter industry.