It's not that it doesn't use water; it's that water is not scarce unless you live in a desert.

As a country, we use 322 billion gallons of water per day. A few million gallons for a datacenter is nothing.

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.

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