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Section 2 <br />Conservation and Efficiency Technical Roundtable <br />1. Water Planning and System Reliability <br />Every water system in Colorado is unique; <br />hence, water system planning and modeling <br />for each system should take into <br />consideration the unique interplay of <br />demands, supply, and storage. <br />Useful concepts for understanding and <br />modeling system reliability are: <br />i. Reliability simply defined is a water <br />supply system's ability to meet the needs <br />of its customers during times of stress. <br />ii. Safe yield (also called firm yield, although <br />the definitions may vary) is defined here <br />as the maximum volume of water that can <br />be delivered by an entire system over a <br />realistic hydrologic period that includes <br />the drought of record. <br />iii. Reliability criteria are the allowable <br />shortages and their respective frequencies <br />that a water provider is willing to tolerate <br />without failing in its service commitment <br />to customers. For example, the City of <br />Boulder's water supply planners have <br />planned their water system to meet the <br />following reliability (assurance) criteria: <br />(a) meet essential water needs against <br />droughts of 1,000-year recurrence <br />interval; (b) meet needs to sustain <br />landscaping against droughts of 100-year <br />recurrence levels; and (c) meet total <br />demand against droughts of 20-year <br />recurrence levels. <br />Some water providers evaluate the "absolute <br />reliability" of their water supply system from <br />a mass balance standpoint by testing how <br />well it performs during a critical drought, <br />based upon historic hydrology data. This <br />concept is similar to safe yield (described <br />above). Some providers prefer the concept of <br />"design reliability," which takes the absolute <br />reliability and applies a "factor of safety" <br />such as assuming there is less storage in their <br />system than actually exists or by using <br />hypothetical hydrology that includes more <br />severe droughts. <br />- Providing for growth in a system and/or <br />increased reliability can be accomplished by <br />(a) adding new supply to increase the safe <br />yield of the raw water system; (b) decreasing <br />the demands of existing customers; or (c) a <br />combination of the two. <br />2. Water Conservation and Drought Response <br />- There are important differences between <br />long-term water conservation programs and <br />drought response programs. <br />- Long-term water conservation programs <br />typically seek to achieve permanent <br />reductions in demand through technical and <br />structural improvements and behavioral <br />changes. <br />- Drought response programs typically seek <br />immediate and often temporary reductions <br />in demand primarily through behavioral <br />changes. <br />- Technical savings (through fixture retrofits <br />and technological efficiency improvements, <br />leak management, etc.) can usually best be <br />achieved through along-term conservation <br />program. While some technical savings may <br />be achieved as part of drought response, <br />these programs often take time to <br />successfully implement and are often not <br />conducive to the immediacy of drought <br />response. <br />3. Water Conservation, Drought Response, Water <br />Supply Reliability, and Demand Hardening <br />- The concept of demand hardening is defined <br />as follows: "By saving water, long-term <br />conservation can also reduce the water <br />savings potential for short-term demand <br />management strategies during water <br />shortages" (Flory, J. E., and T. Panella 1994). <br />- Demand hardening is a consideration during <br />a water shortage if conserved water is used <br />to serve new customers. <br />- Customers who have reduced their demand <br />through technological changes or who join a <br />system as efficient users (such as new <br />FINAL DRAFT 2-11 <br />