Having a closed coolant loop and using evaporative cooling which expends water aren't mutually exclusive. It's possible for a datacenter to manage heat rejection by blowing air over a radiator like a car does, but it's much easier and cheaper to cool by evaporating water.

This can be set up using a closed coolant loop that takes heat out of the servers, then cools back down the coolant by exchanging that heat into a second separate coolant stream. That way you don't need to care as much about the purity of the water you're drawing and evaporating for evaporative cooling, only the first sealed loop gets pumped though your server racks.

This is the type of setup they're talking about with the much discussed xAI datacenter in Memphis, where xAI pinky swears they are definitely going to resume construction on their wastewater treatment plant [1] and use that for cooling instead. It definitely is designed to consume water and evaporate it, not a closed system like a car radiator that puts its waste heat into ≠the air with no evaporation.

[1] https://wreg.com/news/local/xai-to-resume-construction-on-wa...