DENVER (CBS4) – Lawmakers are working to change a decades-old law that prohibits Coloradans from collecting rainwater.

It’s currently against the law — in almost all cases — to put a bucket by a downspout and catch the rain because that water is the property of people downstream. But a bill changes water rights, allowing homeowners to store up to 100 gallons of rain at a time.

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It’s been illegal to collect rain in Colorado for more than a century. It can be directed by changing gutters or grading, but it can’t be collected.

“Many people I’ve spoken to think I’m joking when I tell them that the collecting of the rain off of your roof is illegal,” said Rep. Daneya Esgar, D-Pueblo.

Esgar and Rep. Jessie Danielson, D-Wheat Ridge, say it’s time the law changed. A recent study found 97 percent of rain doesn’t even make it to a stream because it’s absorbed by vegetation or evaporates.

Esgar and Danielson say homeowners ought to be able to collect and use the water where they need it most, as long as they put it back into the ground.

“Water collected through this bill will not even be enough to water the average blue grass lawn in Colorado even once,” Esgar said.

“Anytime that you manipulate that system — any — it affects somebody,” rancher Jim Yahn said.

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Yahn says the study looked at only a small natural area in Douglas County, not municipal runoff. He says even a little water makes a big difference.

“There are people waiting in line for that water, and if they don’t get that little influx from a rainfall event, then they don’t get that water that they are going to put on their crops, that they’re going to use to offset their well pumping,” Yahn said.

Supporters insist the bill will result in more water for everyone by encouraging conservation.

“Perhaps when they see how little water 100 gallons really is, they’ll think twice about how much water they’re using when they turn that faucet on and it comes pouring out to water their lawns,” Danielson said.

Under the bill Coloradans can only use the rain collected outside — on flowers for example.

The state is in the middle of a 10-year study of rain harvesting in both urban and rural areas. Opponents say lawmakers should wait until that’s done.

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The bill passed committee Monday and is headed to the full House.