Our waterways are becoming more and more polluted due to PFAS, plastics, medicines, drugs, and new chemicals made by companies that just hand over the responsibility of cleaning to plants paid for by public moneys. Detecting the different chemicals and filtering them out if getting harder and harder. Could the simple solution of heating up past a point where even PFAS/forever chemicals decomposes (400C for PFAS, 500C to be more sure about other stuff) be alright?
While you aren’t wrong overall, heat exchangers and heat pumps could drastically reduce the energy requirements, perhaps getting the energy requirements down to 4 or even 2 times the national capacity. This doesn’t means that it’s impossible, it just changes how impossible. It also doesn’t change that there would be cheaper ways than just heating all the water, or that those ways would also be cheaper with more efficient heat management systems.