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.42. The land and Water Fund of the Rockies Meeting Water Demand Without Gunnison Water Albuquerque requires that all landscaping associated with new residential construc- tion include no more than 20% high-water using plant coverage or be subject to a water budget that limits landscape irrigation.''' Albuquerque says that this ordinance yielded a 28% reduction in single-family residential water use.''' Some water providers in the Denver metro area achieved savings of this mag- nitude in response to mandatory restrictions in the face of the 2002 drought. But we doubt that those savings are sustainable without these restrictions, some of which are draconian and inefficient. What is needed and, based on experience elsewhere, entirely possible, is a set of incentives, through rebates and rate structure reform, that encourages water users to make long-term investments in water use efficiency improvement. 3. Supply-side efficiency measures There is a wide variety of measures the Front Range can take beyond water conservation to stretch existing, developed water further. a. Effiuent Re-use or Management In general, less than 50% of the water used for municipal purposes is actually consumed. In densely settled regions like Denver and Boulder, only 35% is con- sumed. The remainder returns to the stream in the forms of treated waste water, return flows from irrigation of lawns, parks and golf courses, and subsurface losses from the treated water distribution grid. Effluent Re-Use refers to any arrangement that uses municipal return flows to increase municipal water supplies. There are two ways to accomplish this goal: return flows can be treated and physically reused for potable and non-potable purposes, and return flows can be reused under substitution or exchange arrangements. At present, the Denver metropolitan area generates return flows in excess of its current reuse needs of about 80,000 AFA. These undeveloped flows are expected to increase to 120,000 by 2045.'73 Under Colorado water law, much of this return flow can be reused again and again to extinction. '" In suburban systems, about 50% is consumed and 50% goes back into the municipal supply each time return flows are reused. Assuming that this process continues until all reusable return flows have been exhausted (losing 50% each time it cycles through the municipal system) 120,000 AFA could produce 240,000 AFA of supply. If recycled through Denver Water's distribution system, consumption would be closer to 35%, allowing the 120,000 AFA to produce 300,000 AFA of supply. Non-potable reuse is being implemented by Denver Water, on a small scale, through the construction of a web of "purple pipes" that carry treated wastewater (below drinking water standards) to businesses and city properties for cooling and irrigation.'" These "purple pipe" systems could be expanded to many new develop- ment sites and can sometimes be retro-fitted to large irrigated properties like golf courses and parks.