This is quite amazing. I wouldn't have imagined that someone has had a legal right to the rain that fell on your property but they are dealing with that sort of right in Colorado just now:

Who owns the sky, anyway? In most of the country, that is a question for philosophy class or bad poetry. In the West, lawyers parse it with straight faces and serious intent. The result, especially stark here in the Four Corners area of Arizona, Colorado, New Mexico and Utah, is a crazy quilt of rules and regulations — and an entire subculture of people like Mr. Bartels who have been using the rain nature provided but laws forbade. The two Colorado laws allow perhaps a quarter-million residents with private wells to begin rainwater harvesting, as well as the setting up of a pilot program for larger scale rain-catching. Just 75 miles west of here, in Utah, collecting rainwater from the roof is still illegal unless the roof owner also owns water rights on the ground; the same rigid rules, with a few local exceptions, also apply in Washington State. Meanwhile, 20 miles south of here, in New Mexico, rainwater catchment, as the collecting is called, is mandatory for new dwellings in some places like Santa Fe.

I once know someone who had argued for the right to use of sea ice as a matter of property. The general idea is that a culture makes a legal right to property from that which is important, is limited and can be excluded from the possession of others in a reasonable fashion. Rain? I would have thought this would be an easy source of a black marketeering. And besides we don't really use water so much as delay it.