A comparison of future water supply and demand projections for the Metropolitan Water District of Southern California (MWD) and its water agency customers reveals substantial differences over the next 25 years. Despite recent trends toward greater conservation and efficiency and more local water supplies, MWD expects relatively less investment in local supply, greater reliance on imported water, and higher per capita demands than its member agencies.
Theses mismatches have real consequences for Californians because the plans are used to make investment decisions in water supply projects with multi-million and multi-billion-dollar price tags, which are ultimately paid by taxpayers and water customers. If water agencies overestimate water demand, they run the risk of investing in water supplies that won’t be needed (but still need to be paid for) and sticking customers with higher water bills.
In our new Mismatched report, we find that MWD overprojects annual water demand by 335,000 to 554,000 acre-feet and underprojects local water supplies by up to 229,000 acre-feet compared to the water agencies in its service area. Based on these projections for higher demand and less local supply, MWD anticipates 259,000 to 281,000 AF more in annual imported water sales than member agencies plan to purchase. If more planned local supply projects, such as water recycling and stormwater capture, are developed, imported water sales would drop even lower.
MWD—California’s largest water supplier— provides about 50 percent of the water supply for more than 19 million people living in Southern California. It imports water from two main sources: the Colorado River and the Sacramento-San Joaquin River Delta, both of which are threatened by climate change and growing demands for water from homes, businesses, and the agricultural sector.
The Colorado River Basin has experienced a decade-long drought, which has reduced natural flows and left the basin on the verge of declaring a shortage. At the same time, decades of excessive water diversions have threatened the Sacramento-San Joaquin River Delta’s ability to supply water and serve as a vital ecosystem for hundreds of species of birds, fish, and other wildlife. And hotter temperatures and more extreme droughts from climate change are likely to make matters worse.
We reviewed the 2015 Urban Water Management Plans of MWD and its 26 member agencies. These plans describe how agencies anticipate meeting water needs in the future. Since MWD’s plan covers the entire region, aggregating the plans of agencies in the region should yield comparable results. Yet our analysis reveals stark differences between MWD and local water agencies.
Regional Water Demand
Because of the region’s heavy reliance on imported water and past drought experiences, Southern California has a long history of implementing conservation and efficiency programs. Reducing the water taken from lakes, rivers, and aquifers leaves more water for future use, as well as wildlife and ecosystems that depend on that water. Conservation and efficiency measures also are generally less expensive than developing new sources of water.
Using more water-efficient fixtures and appliances, updating plumbing and building codes, adopting water conservation rate structures, and other measures have dramatically reduced per capita water consumption. For instance, Los Angeles and Long Beach have reduced per capita water use by 35 percent since the 1980s, resulting in lower total water use today even with higher populations. And during the most recent drought, Southern California reduced water use by up to an additional 28 percent. Despite the region’s history and recent efforts to become even more efficient, MWD projects higher per capita demands than local water agencies. For example, in Riverside County and San Bernardino County, MWD’s forecasts exceed water agencies’ forecasts by 40 to 80 gallons per person per day. For the entire region, MWD’s projections of annual demand surpass water agencies’ by 335,000 to 554,000 acre-feet for 2020-2040.
Local Water Supplies
Water agencies use a combination of local supplies—such as groundwater, surface water, and recycled water—and imported MWD supplies to meet demand. In recent decades, agencies have increased investments in local supplies to improve drought resiliency and reduce reliance on imported water. For example, between 1987 and 2009, recycled water use in Southern California more than quadrupled. And local water agencies expect to invest in local supplies even more. For instance, Los Angeles plans to increase annual stormwater capture by 68,000 to 114,000 acre-feet by 2035.
Yet MWD’s plan includes less local supplies than local water agencies’ plans. In 2025, local water agencies estimate about 154,000 acre-feet more than MWD does and by 2040, this difference increases to more than 229,000 acre-feet, primarily due to increased production from groundwater and recycled water sources.
Imported MWD Water
Local water agencies typically exhaust local supplies first because they are generally less expensive. Additionally, local supplies tend to be more drought resilient than imported water, which is supplied by melting snowpack. During the recent extreme drought when we saw record-low snowpack, MWD reduced water deliveries by 15 percent and penalized member agencies for exceeding their allocations.
To become more self-sufficient and reduce reliance on imported water, many water agencies are increasing conservation efforts and expanding production from local water supplies. For example, Los Angeles aims to reduce imported water purchases by 50 percent by 2025, and Santa Monica is striving to eliminate all MWD purchases by 2020.
Due to less water demand and more local supplies, local water agencies project roughly 259,000 to 281,000 acre-feet less in annual MWD purchases in average water years from 2020 to 2040 than MWD does. But these estimates don’t reflect how much lower imported water purchases could fall since many local water agencies only report MWD supplies available for purchase instead of how much water they anticipate purchasing. For instance, if all local water supplies were used before imported water was purchased, annual MWD sales in average water years would be more than 500,000 acre-feet lower than MWD’s projections.
The report also examines differences in demand and imported water purchases in dry years. While the difference between MWD’s and local water agencies’ anticipated imported water purchases in dry years is less, it is still substantial.