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Rainwater Harvesting

Laws in Tucson, Arizona, Santa Fe County, New Mexico, and Colorado (rooftop collection for small capacity wells and rainwater harvesting pilot projects) are setting new standards on the formerly forbidden practice of rainwater harvesting.

Traditionally, western water law has prohibited the capture of rainwater and meltwater from roofs and buildings.

Western Resource Advocates supports rainwater harvesting as a method of reduce dependence on the West's over-appropriated rivers and aquifers. We encourage adoption of this practice throughout the West.

Who Owns Rainwater?

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 Solution

downspout

Allowing homeowners to capture rain that falls on their residences is a 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 percent of rainwater eventually makes it to waterways and aquifers. In wet years the number rises to 15 percent, but in dry years, no rainwater contributes to surface and groundwaters.