I'm not actually familiar with current DC cooling equipment...but I suspect they use a lot forced-draft, evaporative cooling towers ( https://en.wikipedia.org/wiki/Cooling_tower ). That is far more efficient than "dry" cooling (so long as the outdoor humidity isn't too high). But the waste water from it (what hasn't evaporated) has too high a mineral content to be re-used. Unless you ran it through a desalination plant, which would get very expensive.