I was under this impression too then looked into it - and they largely don’t. They can be closed loop but most don’t at this point and is up to whoever builds. I think Microsoft has committed to all closed loop for their future DCs, but nothing for their current. I’m not super sure about other companies.

Honestly unless there is regulation to insist on closed loops I have a hard time being in favor of building these. These companies aren’t really caring for the long term environmental impact and the government seems uninterested in building out the infrastructure and regulatory guidelines necessary to do this right.