Long dependent on well water and supplies sent hundreds of kilometers by canal from the Colorado River, this desert city will soon harvest some of its 30 centimeters of annual rainfall to help bolster its water resources. Under the nation's first municipal rainwater-harvesting ordinance for commercial projects, Tucson developers building new business, corporate or commercial structures will have to supply half of the water needed for landscaping from harvested rainwater starting next year. Already, the idea has become so popular that at least a half-dozen other Arizona communities are looking to emulate Tucson's approach. "What we learned frankly is that we're wasting a lot of water. It's been our tradition here to shove it into the streets and get rid of it as soon as possible," said David Pittman, southern Arizona director of the Arizona Builders' Alliance. Rainwater harvesting is also gaining popularity nationwide, with Georgia, Colorado and other states legislating to allow or expand use of various types. Across America voluntary rainwater harvesting is irrigating plants or being used in other ways instead of merely falling onto roofs, parking lots or pavement and being drained into sewers as wastewater. "There's only so much water. Unfortunately, Americans are terribly, terribly wasteful with water, and we're running out," said Tim Pope, who builds harvesting systems in the San Juan Islands near Seattle and heads the American Rainwater Catchment Systems Association. Water supplies from the Colorado River are likely to decrease from effects of global warming and increasing demands from other states in the West. And groundwater is carefully managed to prevent overpumping the water that supplies the one million people who live in the growing metropolitan city of Tucson. That makes conservation and rainwater harvesting all the more important. Largely rural Santa Fe County in New Mexico has required harvesting using cisterns or similar water-collection structures, pumps and drip irrigation for commercial and residential development since last year. It had allowed passive harvesting, by which runoff is channeled into soil from rooftops, parking lots and the like. That's the approach Tucson's commercial ordinance takes, though active harvesting is allowed, too. Landscaping needs account for about 40 percent of water use in commercial development and for about 45% of household water consumption, "so there is huge potential," said Tucson City Council member Rodney Glassman, who spearheaded efforts to achieve the ordinance. Rainwater harvesting holds particular appeal in the desert because of the combination of drought conditions and limited sources. Glassman, a first-term councilman, campaigned in 2007 for rainwater harvesting in new commercial development and systems that capture water from washing and bathing in new homes. Last year, Tucson's water utility delivered more than 131,000 acre-feet of water, including 26,000 acre-feet of reclaimed wastewater. According to Glassman, experts estimate more than 185,000 acre-feet of rainfall is available per year. An acre-foot is about 326,000 gallons (1.2 million liters), enough to cover an acre (four dunams) 30 cm. deep or supply about two households for a year. Glassman, who holds a doctorate in arid land resource sciences, said he noticed "a giant disconnect between the need and desire for water conservation and public policy at the local level." Passing the rainwater harvesting ordinance "makes conservation the rule rather than the exception," he said. In addition to adopting the harvesting ordinance, Tucson's City Council also approved another measure requiring a plumbing hookup in new homes so that wastewater from washing machines, sinks and showers may be sent to separate drain lines, if homeowners want, at an additional expense. Those lines can be connected to irrigation systems. Glassman brought developers, architects, environmentalists and ecology advocates together, who eventually proposed a law calling for 50% of landscaping needs for new commercial projects to come from rainwater. "We ended up with a compromise, a practical solution that results in 50 percent less water that has to be diverted from our city water system that has to go on desert plants," Tucson developer George Larsen said. "Nobody thinks it's perfect, but everybody winds up thinking it works." A remodeling project at a Target big-box store on Tucson's northwest side reflects the kind of changes the rainwater-harvesting ordinance will bring. Its parking lot and garden borders are being re-landscaped and incorporate some of the ordinance's elements even though it isn't yet required. The plan features 300 mostly native trees, such as palo verdes and sweet acacias, planted in depressed areas amid the 620 parking spaces. Shrubs also will be grown along the site's border areas. Rainfall will run off from the asphalt into the soil strips, sloped lower than the parking bays. "The more that you can depress areas, the more water that you're going to retain," said Eric Barrett, the project's landscape architect. He said the site previously had only about four native trees and some palm trees and one bank of oleanders, with no water retention. "Now it'll hold 15,000 cubic feet [425 cubic meters] of water, which equates to roughly 112,200 gallons [425,000 liters] per rainstorm."