Rainwater Harvesting

New laws in Tucson AZ, Santa Fe County NM, and Colorado (rooftop collection for small capacity wells and rainwater harvesting pilot projects) are setting a new standard on the formerly forbidden practice of rainwater harvesting. Traditionally, western water law has prohibited the capture of rainwater and meltwater from roofs and buildings, but these new laws recognize the reality and practicality of harvesting natural precipitation for outdoor irrigation.

WRA supports the development of rainwater harvesting as a method of reducing our dependence on the West's over-appropriated rivers and aquifers. We encourage adoption of this practice throughout the West.

Who Owns The Water

Because the West is so much drier than the East, a different set of laws was established to govern water use in this arid landscape. Western water law is based on the Doctrine of Prior Appropriation that can be summarized as “first in time, first in right”. When water is scarce, older, more senior water rights receive water first before meeting the needs of junior water users, no matter their location on the river. Capturing and using rainwater before it has the opportunity to contribute to the flow of streams or recharge underground aquifers generally has been assumed to harm the ability of senior water right holders to use their lawful entitlement, but little is known about how much rainwater capture might actually result in stream depletions.

A Common Sense Solution

Allowing homeowners to capture the precipitation that falls on their residences is a common sense solution to some of the water supply problems that plague the West. In this region, more than half of residential water use is directed to irrigate landscaping. This water is diverted from streams or depleted from aquifers, treated to human drinking water standards, pumped through miles of water mains and then used to water lawns and flowers.

Capturing rain and meltwater collected off of roofs and storing it in cisterns to use for irrigation reduces water utilities' depletions from rivers, streams and aquifers. And it also saves the energy required, and expense paid, for utilities to treat water and then pump it to residences.

Furthermore, the argument that senior water users are harmed by rainwater harvesting may have little merit. Studies in Colorado have shown that on average, only 3% of rainwater eventually makes it to waterways and aquifers. In wet years the number rises to 15%, but in dry years, no rainwater contributes to surface and groundwaters.