America Should Harvest a Trillion Gallons of Rainwater

Over the weekend, Burning Man attendees were forced to shelter in place when the usually-parched Black Rock Desert got roughly 3 months’ worth of rain in 24 hours. In August, Tropical Storm Hilary dropped as much rain on some inland areas of Southern California in a single day as they would typically receive in an entire year. In an age of Western megadroughts and dangerous decimation of groundwater throughout the country, recent storms underscore the importance of investing in the capacity to manage, collect, and store water.

Yet much of the national conversation about drought mitigation is going in a different direction. Arizona’s legislature recently called on Congress to explore pumping billions of gallons of water from the Mississippi River to the Colorado. Governments are contemplating major desalination plants. Both approaches are enormously expensive and involve massive logistical, political, and ecological pitfalls.

In the U.S., there’s strikingly little mainstream discussion of scaling what’s arguably the simplest, cheapest and most sustainable solution for harvesting water: catching it from the sky. The time is ripe for a national policy agenda to dramatically scale up rainwater harvesting.

Around the world, humans have been systematically gathering rainwater since ancient times. The technologies are simple: Collect rainwater from rooftops—on homes, warehouses, factories—and send it down gutters into tanks, where it can be filtered and used for domestic purposes, landscaping, or industrial processes. For farms, harvesting rainwater typically means configuring land with slopes and basins that maximize natural irrigation.

Recent studies demonstrate that harvesting even a small fraction of a percentage of rainwater that falls in a given area can eliminate water shortages for domestic uses while also recharging groundwater. Even when collected rainwater can’t be put to use for drinking or landscaping, it still helps mitigate flood risk from storms. And because there’s no utility needed to transport and sell water that’s collected from a roof, rainwater systems can be less costly than traditional utility equivalents—and avoid the carbon emission associated with pumping between locations.

For decades, many states and municipalities banned forms of rainwater harvesting for concerns about quality or worries about harvesters taking water from downstream users. But, in recent years, state after state has legalized the practice—owing to a growing recognition that collected water can be safely used with filtration and that it contributes substantially to conservation.

Still, despite the shifts in regulation, rainwater harvesting is still mostly the domain of off-the-grid subcultures rather than major industrial companies or residential developers.

But that’s changing.

Apple and Toyota recently built rainwater harvesting systems at U.S. corporate campuses. A Ford manufacturing facility now harvests rainwater for plant operations. Because a 50,000 square foot root can collect about 31,000 gallons of water from an inch of rainfall, owners of large warehouses or factories are harnessing economies of scale and driving much of the growth of the practice. In the past several years, cities including Tucson and Austin have passed some of the nation’s first rainwater collection incentives and requirements, trends that could expand rainwater harvesting among homeowners as well.

Today, the main barrier to wide-scale adoption of rainwater systems is financing the upfront cost of installation. But there are models for how to overcome that barrier. Like installing solar power, installing a rainwater system is a one-time investment that makes it possible to reduce overall utility bills—while meeting other goals like resilience and ecological benefits.

Business and government should look to the success of solar in working to scale-up rainwater harvesting. 

Taking cues from renewables legislation, including the Inflation Reduction Act (IRA), states and the federal government should enact tax credits for residential and commercial installations as well as large agricultural projects. Green banks—the mission-driven financial institutions that are proliferating since passage of the IRA—should help provide financing for homeowners and, in particular, affordable housing developers. Governments should install systems on schools and agencies, while advancing their uptake through building codes and other regulations.

One of the biggest advantages of rainwater harvesting as a public policy solution is that it can win bipartisan support. While rainwater can be a popular cause for Democrats concerned with climate resilience, Republicans can advocate rainwater collection without accepting the science of climate change or standing up to fossil fuel lobbyists.

In August, when Speaker of the House Kevin McCarthy was asked about the GOP’s plans for addressing climate change, he spoke about a proposal—backed by former President Donald Trump—for planting one trillion trees.  While the approach has been justifiably criticized by scientific experts for distracting from the necessary work of reducing greenhouse gas emissions, it nonetheless offers a glimmer of hope that there can be some element of bipartisan action on the environment.

Republicans and Democrats should come together to mobilize government and business toward a common goal: build the capacity to harvest a trillion gallons of rainwater annually.

It’s ambitious, but—combining diverse residential, industrial, and agricultural projects, and drawing on the collective participation of homeowners, companies, financial institutions, municipalities, states, and the federal agencies—it’s achievable.

As recent events demonstrate, we’re entering an era not just marked by scarce water—but wildly unpredictable water. We need a bold but practical plan to adapt.