Coloradans may yet get the chance to use those rain barrels for something other than enormous flowerpots.

The General Assembly’s Water Resources Review Committee on Tuesday considered a bill that would allow Colorado residents to collect and use rainwater that comes off their roofs. Colorado is the only state that forbids collecting rainwater.

It’s a revival of an effort from the last legislative session, but the proposal has a very different look than a bill that died on the session’s next-to-last day. The House version of the 2015 legislation would have allowed residents to set up two 55-gallon rain barrels to collect rainwater that comes off their roofs.

State Sen. Jerry Sonnenberg, R-Sterling, who refused to allow the 2015 rain barrel bill to come up for a final vote in May, is proposing a different approach. His bill would address the biggest concern of farmers, ranchers and others who fear that allowing rainwater collection will threaten their water rights.

Sonnenberg’s draft bill starts with the same two 55-gallon rain barrels as the 2015 House version but goes on to set out a number of new requirements and restrictions, including a requirement that consumers would have to install rain barrels above ground and keep the barrels sanitary and free of mosquitoes and other pests. In addition, water utilities would have to grant permission to install the barrels and then would be responsible for replacing the water diverted into them. The draft bill would also limit use of the barrels to buildings with four or fewer units, meaning most apartment buildings and condo complexes couldn’t collect rain.

Drew Beckwith of Western Resource Advocates told the water committee that his organization estimates about 200,000 people would set up rain barrels in Colorado, diverting an estimated 40 acre-feet of water annually. (An acre-foot is about 325,000 gallons.)

Also under the draft bill, water providers would have to make it easy for consumers to register their rain barrels so the state and utilities could track how much water is being diverted.

The state’s doctrine of prior appropriation, embedded in the state Constitution, lies at the heart of many of the provisions in Sonnenberg’s draft legislation. The doctrine establishes that whoever first lays claim to water in a river or stream is designated the senior water-rights holder and gets first crack at the water. Whoever else holds rights to the water, so-called junior water-rights holders, get whatever is left over.

Under the bill, water providers that allow rainwater collection would have to file something called an augmentation plan — an agreement approved by the state’s Water Court that lets junior rights holders diver water “out of priority” without harming senior rights holders.) The bill includes options for replacing the water, including via a substitute water supply plan that would have to be approved by the state engineer.

But water-rights holders get nervous when talk turns to augmentation plans.

Still, Sonnenberg pointed out that most water districts already have augmentation plans in place and would just have to adjust them. “The intent is to make this simple and cost effective and to keep the prior appropriation system whole,” he said.

It involves a trip before the Water Court to change or establish a new augmentation plan, and that’s not an easy process. According to discussion at the committee hearing, a water district that wants to adjust its plan to allow for rain barrel collection will first have to figure out just how much water will be diverted before allowing customers to collect rainwater, a sort of cart-before-the-horse proposition.

It can also be something of a risk to re-open an augmentation plan, said Doug Kemper of the Colorado Water Congress, opening it up to more changes than those related to rainwater collection.

The water committee decided to order Sonnenberg’s proposal into formal drafting. The committee plans to vote next month whether to sponsor the bill although, if members decide against that course, Sonnenberg could carry the bill on his own next session.

— marianne@coloradostatesman.com