That's one of the problems with having an open loop. Cold water comes in and it has a tiny quantity of an infectious agent, far too smaller quantity to be a problem for anyone.

Then Meta kindly warms that water up by running it through lots of hot computers, the bacterium multiply and do so at a rate proportionate to the temperature (if it goes too hot they die but I doubt even an AI data centre is going to get that hot), then the water gets dumped back into the mains water grid complete with all its lovely infectious agents.

You get bacteria growing in closed loop systems as well, that isn't an issue because it's closed loop you just have to clean it out every now and then.

Nice and warm water, good place for it to thrive. The cooling towers in Arizona sometimes has stickers warning about legionnaires disease.

Moreover, is it not the same water that enter the datacenter ?