IIRC they aren't afraid of people collecting runoff from their roofs -- more like collecting all of the water that falls on their land/building artificial reservoirs while starving the downstream watershed...
But the root is, that's not really a thing out here. The runoff from rain like that doesn't tend to make its way into the water system on that go through the water cycle. Out here it mainly evaporates and sublemates. The water that makes its way into aquifers and rivers is almost entirely glacier/snowpack melt.
