I was glossing over that detail, yes. You can pay the municipality for filtered water, or dig a well.

If you dig a well, you probably own the lot, and also own associated water rights. Otherwise, you are paying for water processing and municipal reservoir management by the gallon. That's how it works for people in houses.

Your mistake is assuming a datacenter is more like that, and less like an agricultural consumer. It's the other way around. A data center and/or power plant handles its own water processing, which only involves water rights.