But can anyone take Devil’s advocate here and explain why a state might want to limit or prohibit rainwater collection? I’m struggling.
Surely it can’t just be financially motivated, right?
Here is the scenario: you are the first settler in an area. You settle by a stream and use the water for irrigation or whatever. Then someone settles upstream from you and diverts the water for another use. In many places you have property rights to the flow of that stream based on prior usage.
Yup. If you allow people to "own" rainwater that hasn't even fallen yet, you are going to need some batshit regulations. So don't do that then.
Used to live in a village with a well (acquifer) and pumping station but in the city I live in now, and all the surrounding towns, all the water supply comes from rainwater (via a reservoir and treatment plant) ... like, where else you going to get it from?
It seems nuts to me - a bit like regulating the breathing of air, or restricting the right to look at the sky.
I can only suppose that these regulations protect the revenue of water companies. I can't think of any socially-useful reason for restricting rainwater harvesting, when the rain is falling on private property.
Harvesting all the rain that falls on a floodplain is another matter; that would amount to appropriating an entire river, which in some parts of the world would cause an "international incident".