I am guessing (not asserting) that there is a sort of cap on water used for agriculture. It's possible we've already reached it. (?)

So, on the matter of scale: there likely isn't a cap on water use of these datacenters. Both the heat emission and usage levels for these systems will likely go up unless there is a fundamental technical breakthrough.

On the matter of utility: As a sibling of GP mentioned, the utility of food is clear.

On the matter of polution: I am not remotely read on waste water and contamination due to industrial agriculture. Is this also something where the judgmental scale is tipped in favor of food production vs cooling systems?