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Colorado's Plan For Future Depletions January 12, 1998 <br />Documentation as Required by Cooperative Agreement, . Page 11 <br />Milestones W6-1, W7-1, W84, and Tab 3B(I)E <br />While irrigation water is sometimes changed to municipal use in such a way as to allow the <br />new municipal user to fully consume the historical depletions associated with the prior <br />irrigation use, in practice this does not fully occur due to the following reasons: <br />1. The Water Court process is inherently conservative in order to protect other water users <br />from injury. Consequently, a portion of the historical irrigation depletion is typically "left <br />on the table" during a water rights change proceeding. <br />2. Water rights changes are often done in a single use basis rather than a consumptive use <br />basis due to the relative ease of implementation. <br />3. To fully consume historical inigation depletions, municipal providers must usually rely on <br />exchange operations and must have storage capacity available at the right times and <br />locations. Because of the inherent complexity and inefficiency of this process, full <br />consumption of historical inigation depletions is rarely attained. <br />4. Reuse of Colorado Big Thompson water is prohibited under Federal contract and Northern <br />Colorado Water Conservancy District rules. Therefore, when CBT water is changed from <br />irrigation to municipal use, only a single municipal use is allowed. <br />Because of these factors, the calculation of accretions/depletions from in-basin agricultural <br />conversion is assumed to be the difference in consumptive use between a single municipal use <br />and a single irrigation use of water. <br />5.2.4 Conservation Seasonal accretionsidepletions from new water demands being met by conservation are <br />assumed to be zero in all months. This is because water conservation savings reduce existing <br />municipal consumptive use at about the same level as the consumptive use associated with new <br />mun.icipal use served by conservation savings. <br />Water conservation reduces both outdoor municipal use, which is about 80% consumptive, and <br />indoor use which is about 5% consumptive. Conservation programs to date have achieved <br />approximately equal savings in the indoor and outdoor use sectors. Future programs are <br />expected to follow this 50I50 savings pattern. The saved water is used to meet new municipal <br />water demands, which are typically about 57% indoor and 43% outdoor. Thus, consumptive <br />use from new municipal demands is more than offset by reductions in consumptive use from <br />existing municipal demands. <br />5.2.5 Water Reuse <br />For each region, the accretions/depletions for each month from water reuse are calculated as <br />follows: <br />regional new municipal water use x <br />% of water reuse in each region's water supply mix x