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7A -32 DRAFT URBAN WATER MANAGEMENT PLAN 3. Water Reliability Overview This chapter describes the balance between water demands (Chapter 1) and water supplies (Chapter 2). In particular, it identifies the current level of reliability of meeting current water demands with current sources of water supplies. Then, it shows how future water supply reliability can be improved via water conservation and water recycling. The appropriate level of reliability for the City is a policy question for the City Council, and depends on the level of risk the City is willing to take and how much the City is willing to pay to minimize this risk with respect to the frequency and magnitude of water shortages. 3.1 Current Water Reliability The City is in a high risk, low reliability situation at this time. The City has one of the lowest levels of reliability of the 29 BAWUA member agencies. The SFPUC water supply situation will remain unchanged until at least July 2009 when the existing Master Water Sales Contract expires and is renegotiated. It is difficult to predict the outcome of the renegotiations, but it is unlikely that City will improve its water supply reliability from this source. When the SFPUC declares a water shortage, Redwood City will be required to make relatively large water use cutbacks as specified in the Interim Water Shortage Allocation Plan adopted by the SFPUC and all suburban purchasers (including Redwood City) in 2001, pursuant to section 7.03(a) of the Master Water Sales Contract. Table 3.1 shows the current level of water supply reliability. � Because the future is unknown, reliability must be expressed in probabilistic terms using the best information available. It is important to note that, as part of the 1984 Master Water Sales Contract, the City has a contractual "water supply assurance" of 12,243 acre -feet per year (AFY). However, this amount relates to a legal definition and not an absolute volume guaranteed. In times of shortage, the SFPUC will provide less than the assurance. In non - shortage periods, the City has purchased as much water as it needs. 12 For FY 2000 -01, the City purchased 13,199 AF. From a statistical perspective, given current circumstances for a given year there is a: Water Supply Reliability, Technical Memorandum dated August 15, 2002 by John Whitcomb, Ph.D. The Urban Water Management Act in 10631(c) asks agencies to identify water supplies in average, single dry year, and multiple dry years. In an average year, the City is not constrained in its water purchases given current circumstances. A single dry year is best described as a 10% SFPUC system -wide cutback (1931, 1961, 1977). Multiple dry years are best described as a 20% SFPUC system -wide cutback (1990 to 1992). 22