The Newhall Land and Farming Company and Valencia Corporation were planning a development called West Creek, which would be a mixed residential and commercial development in northern Los Angeles County. Under the California Environmental Quality Act, an environmental-impact report must be completed for any housing development. The environmental-impact report must contain a thorough analysis that reasonably informs the reader of the amount of water available. Los Angeles County (defendant) was the lead agency preparing the environmental-impact report for the West Creek project. The draft environmental-impact report estimated that the West Creek project would demand 2,194 acre-feet of water per year. The draft environmental-impact report also included information regarding the current overall supply and demand of water in the area and the projected long-term supply and demand of water in the area. The supply data included current entitlements of the water suppliers to water from the State Water Project. However, the State Water Project granted entitlements based on its plan to develop facilities to generate 4.23 million acre-feet of water per year. In reality, the State Water Project has not been fully completed and only produces 2 to 2.5 million acre-feet of water per year. The Santa Clarita Organization for Planning the Environment (the organization) (plaintiff) submitted a comment to the draft environmental-impact report, asserting that there is no guarantee that 100 percent of the State Water Project entitlements would be received. In response to that comment, the environmental-impact report was revised to note that future demand might exceed supply, but all future developments would have to prove the availability of water. Therefore, the development of the West Creek project would not result in an unavoidable significant impact on water resources in the area. Los Angeles County certified the final environmental-impact report and approved the project. The organization then petitioned the trial court for a writ of mandate, asserting that the environmental-impact report was inadequate. The trial court denied the petition. The organization appealed.