关于节约用水能节约多少水的争论仍在继续。加利福尼亚用于城市和农业的大部分水是从旧金山湾三角洲出口的。南加州大都会水区（Metropolitan Water District of South California）是该水源的接受者之一，率先开发了可在全州范围内应用的节水最佳管理实践（BMP）。由于居住在150个不同社会经济背景的城市中的大量人口（15000000人），估计南加州BMP节约的水资源是复杂的- 经济和气候条件。MWD-MAIN用水预测系统用于预测选定的57个需水区域内8个BMP的节水量，以代表大都会服务区。BMP的范围从室内管道改造到大型景观水审计。本文描述了MWD-MAIN用于计算节水的最佳管理实践和减少和覆盖系数的发展。结果以每年英亩-英尺为单位表示，与2000年和2010年预计的基本用水量相比，总体减少百分比。 以每英亩英尺美元为单位的预计节水成本表明，BMPs的成本效益有相当大的范围。

Controversies on the amount of water that can be saved by water conservation continue to surface. Much of the water used in California for urban and agricultural purposes is exported from the San Francisco Bay Delta. Metropolitan Water District of Southern California, one of the recipients of this water, has pioneered in developing water conservation Best Management Practices (BMPs) which could be applied on a statewide basis. Estimating the water saved by BMPs in southern California is complex due to the large number of people (15,000,000) living in 150 cities with different socio-economic and climatic conditions. The MWD-MAIN Water Use Forecasting System was used to project water savings for eight BMPs in 57 water demand areas selected to represent Metropolitan's service area. The BMPs ranged from indoor plumbing retrofit to large landscape water audits. This paper describes the development of the Best Management Practices and Reduction and Coverage factors used by MWD-MAIN to compute the water savings. Results are expressed in acre-feet per year and overall percentage reduction from the base water use projected for the year 2000 and 2010. Projected costs of water saved in dollars per acre-foot show that there is a considerable range in the BMPs cost-effectiveness.