Rainwater Harvesting In The Southwestern United States A Policy Review Of The Four Corners States

Todd Gaston
January, 2010

With the passage of the nation's first municipal rainwater harvesting ordinance for commercial projects, Tucson placed itself at the forefront of the national rainwater harvesting movement. The ordinance calls for 50 percent of water used for landscaping on new commercial properties to come from harvested rainwater. Looking forward, the law will require this proportion of water used in landscaping to be increased to 75 percent within three years of the property being legally occupied. The only U.S. law exceeding this scope in required rainwater harvesting is in the U.S. Virgin Islands, where no reliable underground fresh water source is available.

Western states’ water law has not always allowed municipalities to be so welcoming to rainwater harvesting. Until 2009 the state of Colorado deemed it illegal to capture rainwater off of one’s rooftop, as it infringed on the supply of senior water rights holders downstream. Since then, state law now allows for residences with private well entitlements to harvest rainwater. Many in the state legislature are looking to expand the scope of permitted rainwater harvesting based on recent studies showing that most precipitation never makes it to waterways, thereby challenging the “rooftops are tributaries” assumption that has pervaded Colorado state water law for the last century.

The state of Colorado was not alone in its banning of rainwater harvesting. Utah and Washington State had similar laws as of 2009. “Prior appropriation” has dominated western water law since the 19th century, but each state adhering to the doctrine takes a unique approach to water rights concerning precipitation. With the realities of prolonged drought, growing population pressures, and the unpredictability of climate change, the 21st century presents a gamut of water shortage issues for southwestern states in particular. It is not a surprise then that many southwestern states have shown a willingness to review current rainwater harvesting policies.

This paper reviews past and current water law and resultant rainwater harvesting policies in the Four Corners states: Arizona, Colorado, New Mexico, and Utah. State and local municipal policies, along with their legal foundations, are compared and contrasted with the intent of identifying a trend concerning this issue in the southwestern United States. Policy recommendations for the furthering of, or adoption of, rainwater harvesting polices are made based on this analysis. A background of rainwater harvesting is provided including a look at different techniques, the benefits and costs, and a brief history.