"Collected rainwater is generally considered 'gray water,' or water that is not reliably pure enough to drink but can be used to water yards, flush toilets and power heaters. In some states, developers try to include a network of cisterns and catchment pools in every subdivision, but in others, those who catch the rain tend to do so covertly.
In Colorado, rights to bodies of water are held by entities who get preference based on the dates of their claims. Like many other Western states, Colorado has more claims than available water, and even those who hold rights dating back to the late 19th century sometimes find they do not get all of the water they should.
'If I decide to [take rainwater] in 2009, somewhere, maybe 100 miles downstream, there's a water right that outdates me by 100 years' that's losing water, said Kevin Rein, assistant state engineer."