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Just as people use the sun to generate power for their homes, many homeowners capture rainfall for a variety of uses — from washing dishes to watering gardens during dry spells. But rainwater harvesting, as it is known, can be quite controversial — and in some Western states it is akin to theft.

Opponents of the practice argue that if rain or snowfall is captured, less water will flow to streams and aquifers where it is needed for wells and springs. If enough people hijack precipitation, the thinking goes, it would be cheating downstream users who are legally entitled to the water.

Proponents, meanwhile, see rainwater harvesting as a common sense solution to water shortages and storm water runoff – and find humor in the notion that collecting even small amounts of water is outlawed.

In Colorado, for example, it is illegal for residents to divert rainwater that falls upon land they own unless they have explicit permission to do so. Even collecting rainfall in a backyard barrel can technically violate the law.

“The rain barrel is the bong of the Colorado garden,” wrote a columnist in the The Gazette of Colorado Springs. “It’s legal to sell one. It’s legal to own one. It’s just not legal to use it for its intended purpose.”

Colorado’s assembly did ease the state’s restrictions a bit when it recently passed a bill allowing residents in rural areas who don’t have access to municipal water supplies to capture rainwater or snow melt from their rooftops. (See this article from The Times.)

But Jeff Kray, a lawyer with the Marten Law Group who specializes in the legalities of rainwater harvesting, said the law’s passage is hardly a watershed moment.

“Colorado is saying, ‘We’re opening the door to rainwater catchment.’ Not really,” Mr. Kray said. “They’re cracking the door.”

Washington State is also looking for incremental ways to allow rainwater capture without affecting existing water rights. While the state does not require permits for “de minimis,” or negligible, amounts of rainwater harvesting, like the amount that can be captured in a backyard barrel, it is struggling to establish a reasonable cut-off point.

“Is 50 gallons, 300 gallons or 3,000 gallons de minimis? Where’s the number?” Mr. Kray said. “That’s been the major hang-up.”

In contrast, states in the arid Southwest have literally opened the floodgates to rainwater collection.

In Texas, incentives are offered to encourage the purchase of rainwater harvesting equipment, with up to $40,000 in rebates available to businesses that install collection systems.

Meanwhile, in Santa Fe County, N.M. and Tuscon, Ariz., installation of catchment systems on some new buildings is a legal requirement.