[asdff]

I think that's argued a little differently. Rain you collect from your roof is water removed from a watershed which has an impact on everything living in that environment. You aren't allowed to burn your trash in your yard and pollute the 'public' air either, for example.

[beachy]

Thank you for that explanation. Living on rain water, I have always thought those situations were barking mad, now I get it.

[maxerickson]

In the US it's because the water rights aren't attached to the property, not so much because of the environmental impact.

That is, it's a rancher that is gonna get up in your business if you put in a rain barrel, not a cactus.