You're arguing that if there's an available source of water, people should be able to take from it as they choose. But then what incentivizes me to build a plum

You're arguing that if there's an available source of water, people should be able to take from it as they choose. But then what incentivizes me to build a plumbing system (which, if I should build, I would claim that I owned) if anyone could just take from it?