I don’t know the body of law well but in law school I was taught that west of the Rockies, where most of these prior appropriation water rights shenanigans are,

I don’t know the body of law well but in law school I was taught that west of the Rockies, where most of these prior appropriation water rights shenanigans are, it’s generally illegal to capture rain water because it would interfere with others’ riparian rights.