The City of Morro Bay is located on the central coast of California about midway between Los Angeles and San Francisco. In the late 1980s and early 1990s, California suffered a drought. The City constructed a 0.58 MGD desalting plant. The water supply for the desalting plant comes from wells located on the beach fronting the Pacific Ocean. The plant began operation in early 1993. The desalter operated for several months and was then shutdown following the "miracle March" rains. In 1995, there was again a shortage of rainfall and the desalter was returned to service. However, high precipitated iron concentrations in the well water supplied to the desalter required changing the cartridge filter elements at intervals of about 1/2 hour. It was impractical to operate the desalter because of the cost of changing the filter elements and also because there was insufficient cartridge filter capacity to maintain feedwater flow to the RO equipment because the filter elements were having to be changed too frequently. The City received notice that the supply of imported water from the California State Water Project was to be interrupted for at least one month beginning about November 1, 2002, so that maintenance of State facilities can be accomplished. Less than normal rainfall and contamination of some of the City's well water limited the City's other water supplies. It was determined, therefore, to use the desalter to meet the City's water needs. However, it was first necessary to reduce the iron problem. Boyle Engineering was retained to recommend a method to solve the iron problem. Two solutions were pilot tested for a short period of time that included: addition of chemicals (acid and a reducing agent) in an attempt to redissolve the iron that accumulates in the cartridge filters; and, filtration to remove the iron ahead of the RO system. The pilot tests indicated that installing an iron filter to treat the incoming well water would be the most economical, reliable means of solving the iron problem. Accordingly, in late summer of 2002, the City determined to install such a filter. Due to the approaching shutdown of the State water supply, the City adopted a "fast-track" approach to designing and installing the filter. Includes tables, figures.