State Rainwater. As insane as it sounds in some places it's illegal to capture rainwater that falls on your property. In case you live on one of the non-insane places this is pretty nice: DIY Rain Collector. There is a little hope for Colorado though:

Colorado had some of the nation’s strictest rainwater harvest laws, essentially prohibiting the practice. In 2009, two laws were passed that loosened restrictions.
CO SB 80 allowed residential property owners who rely on certain types of wells to collect and use rainwater. Colorado Revised Statutes §37-90-105
CO HB 1129 authorized 10 pilot projects where captured precipitation was used in new real estate developments for non-potable uses. Colorado Revised Statutes §37-60-115