It goes into the soil and can take a long-ass time to get back into any our supply. Yes, it's still on earth, but it's no good to you if it's locked up in the soil or the polar icecaps. And that's not to mention the ridiculous ways we pollute water that make it very difficult if not impossible to recycle. This stuff really isn't as simple as just drain the lakes and rivers. We absolutely could run out of fresh water, and pumping it into data centres is a terrible idea.