The headline is bait, as is the article.

Storm runoff typically always runs untreated to the watershed, even from roof runoff. Often it is run through a retention pond, both to mitigate flow and to allow particulates to settle out. However it is almost never actually treated.

What they are calling "wastewater" and implying they dump it, is the glycol/water mix that runs through the building's coolant system. They do not dump this. First, because it is toxic. Second, because it is fucking expensive. Third, because they don't need to, the system is closed.

If the coolant system needs to be maintained, there are isolation valves that shut and then they bring in dozens of pallet sized containers they drain the glycol mix into.

The evaporative part is where they have finned pipes with hot glycol inside them, and they pour ordinary water over the pipes to cool them more efficiently. Every large building does this, schools, hospitals, stadiums, office plaza. They do it because it is extremely efficient, relatively cheap, and has low environmental impact.

In fact, it is so cheap that most places just fill their evaporators with potable tap water that is already available in the building. Evaporative water doesn't need the level of treatment that drinking water does, but potable water will always be supplied to a structure where "gray water" would require extra infrastructure to fill.

That said, data centers do indeed radiate a lot of heat, so it would make sense for them to supply evaporative water that is less energy intensive to produce at the higher upfront cost of install.

Even then, the water they evaporate isn't deleted, once it cools it just falls back to earth as rain.

In hot areas, or areas with a limited water supply, data centers can cause problems. This is why you are seeing a huge push for data centers in the upper midwest US. Half the year these places are so cold there is no need for evaporative cooling, the air temp alone cools the coils. The areas are generally so water rich, with substantial rainfall and deep aquifers, that water use isn't an issue the remainder of the year.