For years now, Coloradans have been fighting over the seemingly innocuous rain barrel. Environmentally conscious and thrifty residents say they should have the right to catch as much rain as they please, while agricultural interests argue that doing so is tantamount to stealing water from its rightful owners. The same battle has played out throughout the West, but Colorado is the last remaining state where barrels are banned outright—for a few more days, anywayOn April 1, the state legislature passed a bill to permit residents to catch rain in measured quantities, and Governor John Hickenlooper is expected to sign it.

Coloradans will no longer have to hide their downspouts and barrels for fear of being fined, but the issue is hardly settled. The forthcoming law keeps historical water law intact, while opening a crack in the once unbreakable water doctrine by allowing two 55-gallon barrels per residential property. It won’t be long before residents lobby for the right to collect more, and yet, water is only becoming scarcer in the West. Persistent droughts, exacerbated by climate change, and a rapidly expanding population will only intensify the debate over rain-catchment laws. The water wars have just begun.

“The controversy over the rain barrel proposal is not really about rain barrels,” said Douglas Kenney, director of the Western Water Policy Program at the University of Colorado, Boulder’s law school. “It’s about what some people see as a dangerous precedent in terms of changing the water rights regime. ... The stakes are very high.”

Colorado has a deeply rooted system of “prior appropriation”—finder’s keepers, essentially—which for over a century has governed how water is allocated in the state and much of the West. During the Gold Rush of the mid-1800s, miners flooded the West, settling next to rivers and streams to pan for gold. To ensure newcomers wouldn’t stake claim to the same water, the system of prior appropriation was established, creating the “first in time, first in right” standard that gave priority to “senior claims” over water. Those who arrived in the area more recently had “junior” rights, and newcomers were only permitted to use water left over after the first arrivals had their share. Settlers who held the most senior water claims were able to use as much water as they could put to beneficial use”—essentially, not to waste it.

After the Gold Rush peaked, westward migrants moved in to establish agricultural communities, and prior appropriation—which was written into Colorado’s constitution and that of five other Western statesprovided some level of risk protection. “No one would come out West and build a farm or a business, or anything, and invest all that time and effort if they thought someone else would come by ten years later and start using the water that the original settler had depended on,” Kenney said.

The rain barrel predated deep household wells. Settlers installed eaves and troughs to collect water to use for laundry and gardening.Library of Congress Prints and Photographs Division

Today, agriculture in Colorado uses nearly 90 percent of the state’s water. Meanwhile, rain catchment has become increasingly popular since the dawn of the environmental movement, going mainstream in recent years and putting pressure on Western legislators to reconsider their ancient water laws. In 2009, Colorado passed a law allowing limited barrel collection by residents who relied on private well water. Since then, attempts to further legalize rain catchment has created what the Denver Post called a legislative storm. The state Senate allowed a broader rain barrel legalization billsimilar to the one passed this year—to expire. The committee chairman of the state Senate Agriculture, Natural Resources, and Energy Committee has opposed rain barrel bills for years, partially because of how they might affect agricultural interests. While some small-scale farmers have expressed their support, the agricultural industry objected to this bill. This year’s bill passed in part because of two amendments: one that guaranteed rain barrels would not technically be considered a water right, and the other promising the state would monitor the affects of the barrels on existing water rights.

More than three-quarters of the Western population live in cities, which are expected to grow by over 10 million people over the next 30 years. Farmers are rightly wary that urban centers will hold increasing sway over the region’s scarce water. Prior appropriation is a lifeline to traditional livelihoods like farming, but agricultural areas in Colorado are already facing a strain on water sources: There’s not enough water to divvy among all residents with legal claims. By 2030, Colorado is expected to have a water shortfall of 118,00 acre feet (one acre foot is enough water for a family of four for one year).

With the new Colorado law, rain barrels may provide some relief where Western tributaries cannot. The Colorado River, one of the most critical water sources in the West, supplies water to 30 million people. But climate change, in the form of rising temperatures, has reduced flows in recent years. These changes will continue to reduce water accessibility in the Upper Colorado River Basin, which encompasses parts of Wyoming, Utah, Colorado, Arizona, and New Mexico. According to environmental law professor A. Dan Tarlock, prior appropriation “may be further undermined by the uncertainties of the regional and watershed impacts of global climate change.” Kenney, though, doesn’t see prior appropriation going away any time soon, even in areas where water is even scarcer, like California. “If that drought were to continue another year or two and the cities were to get really desperate, then maybe some reforms that people always assumed were totally inviolable, then maybe they become possible,” he said. “I just don’t see it happening.”

Colorado is just now catching up to other states that have incorporated progressive rain conservation with prior appropriation. Arizona allows rainwater catchment, and since 2008 Tucson has required it for new commercial projects. New Mexico offers incentives for rainwater catchment. Washington legalized barrels in 2009 and Utah in 2010.

“If every little reform is going to be that big of a fight, then we have problems,” Kenney said. “You can’t spend years fighting over rain barrels.”