The fact that a datacenter is evaporating X gallons of water in a period implies that a datacenter is ingesting X gallons of water (if less, the datacenter dries out, if more the datacenter floods) - meaning X gallons are now locked out of the water cycle. Meaning it rains back down and gets slurped back up.

This is under the happy assumption that all used water evaporates into a cloud directly above the source region, which rains back directly.

How much water is contained inside the datacenter at any given moment? That's how much water is taken from circulation by this datacenter. Is it enough to worry?