For the second year in a row, a legislative storm is brewing in Colorado over who legally owns drops of rain.

A bill that would allow gardeners to store 110 gallons of runoff from their roof in up to two rain barrels passed on a 10-2 bipartisan vote in a House committee Monday. Republicans in the state Senate let a similar bill expire without a vote on the chamber floor at the end of last year’s session.

Opponents cited state water law that says rainfall must be allowed to move unabated back into the ecosystem to feed aquifers and reservoirs for those who hold expensive water rights.

In theory, proponents say, when the rainwater goes on gardens or lawns, it would then return to the larger environment. In the bargain, rain-barrel users would get a sense of how little it rains in Colorado and how much water they use on their property,

“This is a simple tool that will encourage water conservation and encourage people to use water wisely at their homes,” said Rep. Jessie Danielson, a Democrat from Wheat Ridge, who is one of the bill’s sponsors.

Colorado is the only state that bans rain barrels and is one of just four states that restrict so-called rainwater harvesting, joined by Arizona, Oklahoma and Utah, according to the National Conference of State Legislatures.

Reagan Waskom, director of the Colorado Water Institute and chairman of the Colorado State University Water Center, said an experiment showed no detectable impact on downstream runoff. Nearly all of it is absorbed in the soil, just as it would if it was not captured.

CSU is neutral on the bill, he said.

“The water that’s captured in a rain barrel would be captured in the soil, anyway,” Waskom said. “You’re not going to be able to measure it.

“It’s very important, every drop, to the downstream users,” he said.

Sen. Jerry Sonnenberg, R-Sterling, a chief opponent last year, said the bill would face problems in the Senate if it does not acknowledge the state’s prior appropriation doctrine, which ensures those with senior water rights get their share. The bill also must identify a state agency or other authority to see that happens, he said.