Can we all just catch raindrops where they fall? – the state of rainwater harvesting in the Colorado River Basin

Green Roof in Denver, CO | © US EPARainwater harvesting is a valuable tool to increase local water supplies but must also be carefully considered in the face of complex western water laws and impacts on groundwater recharge and river flows | © US EPA

Growing up in Los Angeles in the 1990s, I remember the severe water shortages. Almost overnight, everyone was installing showerheads that could shut down the water flow mid-shower and placing bricks in their toilet tanks to decrease the amount of water used per flush. And yet at the same time, I would go for walks in the occasional rains that we did get and be up to my thighs in runoff and flooding from the storm.

Looking back, I wonder why we weren’t catching more of that rain to store and use during the dry season. A combination of conservation and more efficient use of local water will be critical to address the increased demand as the population in the west grows and the available supply diminishes due to the effects of climate change.

While conservation and efficiency should top the list of solutions to be used to ensure reliable water supplies for the water-limited western United States, green infrastructure techniques such as rainwater harvesting are also good strategies to increase local water supplies, decrease demand, and increase water quality. In the face of recent droughts and concerns about decreasing water supply and increasing population, many western states started considering and passing legislation to legalize rainwater harvesting.

Many of the seven states within the Colorado River Basin now allow residential and commercial properties to install green roofs, rain barrels and cisterns, or other green techniques to capture and use water on-site. In fact, some regions are aggressively requiring large-scale implementation of these techniques; Santa Fe County in New Mexico requires the installation of rainwater harvesting equipment on both residential and commercial sites and Tucson, Arizona requires that new commercial developments harvest enough rainwater on-site to meet half of their landscaping requirements. Even in states with more restrictive policies such as Colorado, where rainwater harvesting is limited to a very specific subset of users, there is a growing movement towards allowing the use of these techniques to manage stormwater while preventing impacts to existing water rights.

Water rights in the water-limited western United States are very complicated, and protect the rights of the people who currently hold the water rights. This makes sense given the limited water supplies, and prevents someone from buying property along a stream, damming it, and thus preventing any water from getting to downstream users. These water rights, and the climate realities that created the need for them, mean that rainwater harvesting implementation needs to be carefully planned to ensure that these systems don’t remove too much water out of the Colorado River system.

As with any type of water infrastructure, rainwater harvesting efforts should be adapted to fit local needs and to take into account local hydrology. In 2013, the Colorado was listed as our nation’s most endangered river in part for poor water management. While rainwater harvesting offers an important tool, if used without consideration of regional or local contexts, it could exacerbate supply concerns.

For instance, rainwater harvesting makes a lot of sense in areas like Los Angeles and San Diego, which use water that comes from the Colorado River but are not located within the Basin itself. Any water harvested in these areas decreases demand on the Colorado River without also reducing the supply. Rainwater harvesting is one among the many techniques of increasing local water supply that should be thoroughly explored and implemented in the Colorado River Basin.