colorado no longer has that law it was changed june of 2009.
http://www.nytimes.com/2009/06/29/us/29rain.htmlstill illegal in utah unless you own water rights on the ground you own..
but i believe even there you can now get a permit even if you dont own the water rights.
these laws came out of the water rights laws of the old west,they are not anything new. in fact most of the new laws concerning rainwater harvesting are going the opposite direction.
for example,santa fe now requires all new dwellings to have a water catchment system..