Historical Water Use in Los Angeles
Water use in the City of Los Angeles peaked in 1986, at just over 700,000 acre-feet per year (AFY). What followed was five years of severe drought, widespread water shortages, and the implementation of mandatory conversation measures. Due to conservation, a boost in rainfall in 1992 and 1993, and tough economic times, water use dropped by more than 17 percent in the following years.
Since the early 1980s, the City has invested millions of dollars in conservation measures, particularly the installation of low-flow toilets and shower heads. Thanks to these efforts, L.A.’s water demand is about the same as it was 25 years ago, despite a population increase of 1 million people.
Historical water use data show that the largest customer group falls in the residential category. For fiscal year 2006-07, residential customers (multi-family and single-family) accounted for 68 percent of the water demand. The second largest group are commercial customers (17 percent); followed by governmental (7 percent), industrial (4 percent), and non-revenue generating uses (4 percent).
Impacts on Historical Water Sources
Although these water resources have served the City well for decades, several factors have converged that threaten the long-term availability of these supplies. Climate conditions such as consecutive years of below-normal snowfall and drought can greatly impact the availability of these water sources. That, along with environmental commitments, has severely impacted historical water supply sources.
Eastern Sierra Watershed
Over the last two decades, the City’s water deliveries from the Los Angeles Aqueduct (LAA) have dropped dramatically due to reallocation of water for environmental mitigation and enhancement in the Eastern Sierra. From 1995 through 2000, the City received 63 percent of its water from the Eastern Sierra through the LAA. From 2001 through 2004, however, only 34 percent of the City’s water came through the LAA.
Each year, the snowpack in the Eastern Sierra varies, and dictates the quantity of water delivered by the LAA. To illustrate, Figure 2 shows the historic water supplies from the LAA, MWD, and local groundwater. Note the significant annual variations in LAA deliveries that are inversely proportional to MWD water purchases, highlighting the City’s strong reliance on MWD, especially during dry years.
Reductions in LAA deliveries are largely due to the reallocation of water for
environmental mitigation and enhancement. Among these environmental requirements are: the State Water Resources Control Board Mono Lake decision, which permanently limited LADWP’s ability to export water from the Mono Basin; implementation of the Owens Lake Dust Mitigation Project; rewatering of the Lower Owens River, and a number of other environmental restoration projects in the Owens Valley that require water.
MWD Purchased Water (Sacramento-San Joaquin Delta and Colorado River)
MWD is a consortium of 26 cities and water districts that provides wholesale water supplies to Los Angeles, Orange, San Diego, Riverside, San Bernardino and Ventura counties. MWD currently delivers an average of 2.3 million acre-feet of water per year to a 5,200 square-mile service area. MWD’s sources of imported supplies are from the Colorado River, the State Water Project (through the Sacramento/San Joaquin River Delta), local surface and groundwater storage, and storage/transfer agreements with Central and Sacramento Valley agencies and Colorado River agencies. Los Angeles
typically purchases MWD water to make up the difference between the demand and other City water supplies. Over the last two decades, while these resources have proven a key component of our water supply, they are also subject to uncertainty due to climate variability and environmental issues.
The current environmental crisis in the Delta has led to a Federal Court decision that will result in MWD receiving up to 30 percent less of their anticipated State Water Project deliveries. Although water allocations have been deferred for now, the MWD Board has approved significant increases in wholesale water rates to address the increased costs of importing water and purchasing water from others.
Despite concerns about ongoing water shortages and higher costs, MWD has upheld its pledge to plan for emergencies and natural disasters throughout this region. The agency has approximately 1.7 million acre-feet in surface and groundwater storage accounts – including Diamond Valley Lake near Hemet – and 600,000 acre-feet of storage reserved for emergencies. In total, this reserve of water supplies buffers the severity of a potential shortage, allows for a less severe water shortage allocation if required, and keeps the region prepared for a major earthquake or other events.
Los Angeles relies upon local groundwater for an average of 11 percent of its total water supply, and historically more during emergencies and drought years. The City’s water rights pertain to groundwater basins in the San Fernando Valley as well as the Central and West Coast Basins. However, groundwater contamination in the San Fernando Valley, where the majority of the City’s groundwater supply is produced, has severely limited water available for pumping.