Just because some countries waste a lot at present time does not mean it's available as a resource indefinitely.

The problem is you don't just use that water and give it back.

The water gets contaminated and heated, making it unsuitable for organisms to live in, or to be processed and used again.

In short, when you pump back that water to the river, you're both poisoning and cooking the river at the same time, destroying the ecosystem at the same time too.

Talk about multi-threaded destruction.

No, you're making that up. Datacenters do not poison rivers.

To reiterate, I work in a closed loop DLC datacenter.

Pipes rust, you can't stop that. That rust seeps to the water. That's inevitable. Moreover, if moss or other stuff starts to take over your pipes, you may need to inject chemicals to your outer loop to clean them.

Inner loops already use biocides and other chemicals to keep them clean.

Look how nuclear power plants fight with organism contamination in their outer cooling loops where they circulate lake/river water.

Same thing.

Dude you can’t fight Dunning Krueger. They all think they’re experts in everything now.