http://www.latimes.com/news/nationworld/nation/la-na-contested-rainwater18-2009mar18,0,5585599.story

Executive summary: If you live in Colorado and have a rainbarrel that collects rain and snow runoff from your roof, you are violating state law in Colorado. Precipiation is required to seep into the ground and/or flow unimpeded into the creeks for all to share, becoming the property of all.

Western states have strange water laws.