I would dispute the water will ever be returned to the water supply. Cooling towers require corrosion inhibitors, other additives, and deposit other inert and toxic materials that must be purified and never will be.
Sure, some fraction of withdrawn water is retained due to contamination. That’s counted in the consumption numbers of the source study? The operative question is still whether DCs and related power generation consume a concerning about of water.
This summer I biked past one of the purification plants that you say never will exist.