Water comes from the sky but then is channeled into streams, lakes, and the like in a chain. Human civilization springs up in places assuming that chain will be unbroken.
If someone does something upstream that prevents the normal amount of water from getting downstream, then there are negative consequences to the whole of society. As such, the people downstream do have a say, via their governments, in what the people upstream do.
Rainwater is basically “upstream” of *everything.* Collecting rainwater is therefore a bit like building a dam without asking anyone else who lives down the river.
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