Next is open loop cooling using secondary loop. Take a river, lake or sea. Pump some water from it, pass through heat exchanger and pump back out. Manageable for most of the year. Worse version is pump ground water and return it to these. Depletes the ground water...
And finally evaporative cooling. Which is boiling, but not at boiling point. Water goes to sky. No immediate return to local ground water or downstream the river... In this case you actually do in sense use up the water. Kinda like burning fossil fuels returns co2 to atmosphere. It will later turn to biomass, but that is a separate cycle.
Rain is more of a location problem. The evaporated water returns as rain quickly, but maybe somewhere else, such as over ocean. And the aquifer compresses and loses water retention ability.
You can use it for irrigating your lawn but not for vegetables, especially not if you plan on selling them. But 'light' gray water requires relatively little treatment before you can use it again, however this could still be quite expensive compared to just letting it go. I wonder if they've done any quantitative research on this that's public.
https://www.scaleway.com/en/blog/making-the-energy-efficienc...
That's why central heating systems that run 'low' every now and then stoke up to 60 degrees or more on the secondary circuit for tap water.
And data centers are the perfect location, endless 35 to 45 degree water. Cooling towers are the main problem for this, another is aerosols of water that has been sitting in the sun for a while, for instance in a garden hose exposed to the sun.
Drinking water from the mains is metered, so it is observable from the business perspective. Life finds a way. Heat exchangers and datacenter plumbing absolutely breed life and put things into the water that were not there when it was pumped in.
Imagine if a datacenter used a shady supplier of pipe that used, say, lead in their alloy. Do you want that datacenter grey water going into crops?
But yes, it rarely enters the building via different pipes. I'm sure that's a thing somewhere too.
It's a bad idea to drink hot water from the tap because of the concentration of metals that accumulate in the water heater. Don't assume that a little metal in your water is perfectly safe. As for agriculture, now the metals can concentrate in your lettuce.
And, as other commenters have pointed out, what else is in there? How about Legionnaires Disease?
The main reason we are talking about this is because 'environmentalists' (which in itself gives a hint about the levels of expertise) are worried, they are not worried for no reason. Listing a multitude of reasons should at least make you pause about whether or not they are sincere in their concern.
The degree to which industry would wreck the environment if we let it is by now very well documented. But the EPA has been gutted and lots of safeguards have been abandoned in the name of 'progress'. This is not without risk and I am very happy that in spite of all this a lot of people are still willing to speak up and to make sure that at least the worst excesses are curbed.
You can approach this with curiosity to try to learn about the subject and to try to understand what drives the worry of people that have studied this stuff for a long time. These are not just idle musings. Or you can put up a barrage of questions effectively casting doubt on anything that might be of concern.
I am all open to there being problems with re-using water used to cool datacenters (hence my question). But 1) "it boils" defies common sense, no component in a computer should run at >100 degree celcius continuously, so I find it hard to believe that datacentres boil water (and I would have noticed the big cooling tower on the side of them). 2) Legionnaire disease is certainly a big deal in residential buildings with stagnant warm water, sitting in pipes sometimes for days until someone takes a shower. I fail to see how it is a major issue for a continuously flowing industrial application where the water spends very little time at elevated temperature and is continuously flowing before being released into colder water. 3) "contact with metal is bad" certainly doesn't come from someone who has seen the water supply chain in the UK or any European country with ancient infrastructures. Many of which are still made of lead. 4) "water is then not suitable for human consumption", well neither is the water in a lake. All drinking water has been filtered and sterilised. I would be surprised water used for cooling has been treated that way. So unclear to me why there would be any expectation that the water coming out of a datacenter should be any cleaner than the water coming out of a lake.
Now there is common sense, and there are regulations. The two often form a perfectly disjoint venn diagram. So I am happy to believe that there are regulations resulting in absurd situations. But from an actual risk point of view, I don't see how a datacenter "consumes" water, in any comparable way than a swimming pool, agriculture, chemical plants, or gardening, where the water cannot be used for anything else after that. To me it is more akin to a nuclear power plant, which releases water at a slightly higher temperature (despite actually boiling it), and therefore has a fairly limited impact on the water supply.
Exact values matter. Some power plants had been found dumping +10 C water into lakes/rivers, while they had permit only for +5, and it totally destroyed local ecosystem. And most efficient (in terms of money) is evaporation cooling, where at least part of water is "lost".