Rainwater harvesting is a great way to help out the environment while reducing water bills. It's one more way Americans can help reduce potable water use.
However, states such as Colorado have, in most cases, banned the collection of rainwater from roof gutters due to misguided fears of stream depletion and violation of water rights for states that are downstream.
In a study done by the CWCB and Douglas County, CO, it was found that on average only 3% of water that fell on an undeveloped test site returned to streams or rivers. Thus, it can be argued that demanding that all water caught in rain gutters and other drainage systems be returned to the state is infringing on the land owner's water rights.