[JeremyNT]

Really, you have to isolate the variable you care about here, which is 'how much energy is spent on cooling.'

Consider, if you can achieve a fully passive cooling solution by dropping a datacenter into a lake, you've reduced the energy consumption in service of cooling by 100%.

(In reality, water cooling isn't "free," but I'm willing to bet the amount of energy required to dump heat into surrounding water is a whole lot less than the amount of energy spent for the compression cycles and forced air of above-ground HVAC systems. Water cooling using direct application of chilled water is already a thing, using lakes or retention ponds as places to dump heat; what being at the bottom of a lake gives you is a more consistent and proximate source of cool water than you might expect from a current chilled water distribution system)