All she wants is the rain water that lands on her roof. She lives with her husband and two children in a solar-powered home in rural San Miguel County. Committed to promoting sustainability, Kris Holstrom grows organic produce year-round, most of which is sold to local restaurants and farmers markets. On a mesa at 9,000 feet elevation, however, water other than precipitation is hard to come by.

So Kris did what thousands of farmers before her have done: She applied for a water right. Except instead of seeking to divert water from a stream, she sought to collect rain that fell upon the roof of her house and greenhouse. To her surprise, the state engineer opposed her application, arguing that other water users already had locked up the right to use the rain. The Colorado Water Court agreed, and Kris was denied the right to store a few barrels of rainwater. If she persisted with rain harvesting, she would be subject to fines of up to $500 per day.

How could this happen?

Like other western states, Colorado water law follows the prior appropriation doctrine, of which the core principle is “first in time, first in right.” The first person to put water to beneficial use and comply with other legal requirements obtains a water right superior to all later claims to that water.

The right to appropriate enshrined in Colorado’s Constitution has been so scrupulously honored that nearly all of the rivers and streams in Colorado are overappropriated, which means there is often not enough water to satisfy all the claims to it. When this happens, senior water-right holders can “call the river” and cut off the flow to those who filed for water rights later, so-called “juniors.”

Overappropriated rivers are not unique to Colorado. Most of the watercourses in the West are fully or overappropriated. Yet other western states allow or even encourage rainwater harvesting. The obstacle for aspiring rainwater harvesters in Colorado is not the state constitution. It speaks only of the right to divert the “unappropriated waters of any natural stream.”

The problem arises because Colorado’s Supreme Court has given an expansive interpretation to the term “natural stream” and coupled that with a presumption that all diffused waters ultimately will migrate to groundwater or surface streams. And because most streams are overappropriated, collecting rainwater is seen as diverting the water of those who already hold rights to it.

How is a roof a “tributary”?

Applying this legal fiction to Kris Holstrom’s effort to grow food at home, the state engineer argued that her roofs were “tributary” to the San Miguel River. Because the San Miguel River is “on call” during the summer months, Kris’s rain catchment would, the state engineer argued, “cause injury to senior water rights.” The court agreed, even though there was no proof that the water dripping from Kris’s roof would ever make it to the river.

If Kris wanted to collect rainwater for her gardens, she’d have to pursue an augmentation plan and convince the state engineer and water court that she could replace 100 percent of the precipitation captured. Not only did she have to return to the stream every drop of rain she collected, she would have to pay for a complex engineering analysis to prove that her augmentation water would return to the stream in a timeframe mimicking natural conditions.

She didn’t even try. “The farm doesn’t make enough money to pay for an engineering analysis,” she said. Indeed, it’s difficult to imagine a situation where it would make financial sense to harvest free rainwater that has to be replaced with another source of water.

The notion that you can’t utilize the rain falling on your roof might be easier to accept if you really were interfering with senior water rights, but in many situations it just isn’t true. In Kris’s case, most of the rain she collected would have evaporated or been transpired by native vegetation long before it ever reached the San Miguel River.

Hardly a drop in the bucket

A recent study commissioned by Douglas County and the Colorado Water Conservation Board has confirmed that very little precipitation that falls on an undeveloped site ever returns to the stream system. The study focused on an area in northwest Douglas County, where the average annual precipitation is 17.5 inches. In dry years, 100 percent of the annual precipitation is lost to evaporation and transpiration by vegetation. In wet years, a maximum of 15 percent of the precipitation returns to the stream system. On average, just 3 percent of annual precipitation ever returns to the stream.

Despite this hydrological reality, Colorado law requires anyone wanting to use rainwater catchment to send to the stream an amount of water equivalent to 100 percent of all precipitation harvested. That is, in effect, a gift to prior appropriators paid for by folks trying to live more sustainably.

An effort to address this problem stalled in the Colorado legislature this past session. A bill by state Sen. Chris Romer, D-Denver, would have allowed rural residents not on a municipal water system to store rainwater in cisterns up to 5,000 gallons. The bill also would have authorized 10 pilot projects where new housing developments could collect rainwater from rooftops and other impermeable surfaces. But even this tepid effort to update water law was sent to committee for further study.

The committee should use this study period to produce a bill that takes a more aggressive approach to water sustainability. The first thing is to make sure the benefits of rainwater harvesting are not dissipated into oversized yards filled with water-guzzling bluegrass. A serious effort would limit harvested rainwater to food production and Xeriscaped yards.

A resource down the drain

Even greater benefits could be achieved by promoting wide-scale rainwater harvesting in developed areas. Traditional land development practices typically direct runoff from roofs and other impervious surfaces to pollutant-laden streets and parking lots, and then toward storm drains.

Both of these problems would be ameliorated if all buildings were equipped to catch rainwater for later use. Additional benefits could be realized if the water collected from rooftops was brought inside for nonpotable uses. Rainwater that would otherwise be lost to evaporation or storm drains could be used in toilets and washing machines, and then sent to the treatment plant, thereby bringing more water into municipal water systems.

Colorado is expecting 3 million new residents by 2035. At the same time, climate change may be conspiring to exacerbate the water woes of all of the states served by the Colorado River. Rainwater harvesting is no panacea to deal with water shortages, but it should be part of a multifaceted approach to a looming crisis.

Fully utilizing precipitation where it falls reduces the demand on other water resources, leaving more water in streams or aquifers. The most important benefit of a legal change stimulating wide-scale rainwater harvesting may be its fostering of a new water ethic. People who make a personal effort to collect and utilize rain are less likely to waste water or tolerate public policies that allow waste by others, such as inefficient irrigation or inappropriate residential landscaping.

When people are maintaining gutters and cisterns to flush their toilets or grow their gardens, they are more likely to appreciate the importance and scarcity of water. They might finally say no to headlong growth that shows no regard for long-term availability of future water supplies.

Colorado should embrace rainwater harvesting. The legal fiction that all rain is tributary to a stream should be abandoned. Others should not be allowed to own the rain that falls on your roof before you can use it for reasonable domestic uses.