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| Fig. 1: Map of the California State Water Project. [1] (Source: Wikimedia Commons) |
The California State Water Project (SWP), administered by the Department of Water Resources (DWR), ensures that customers in regions of the state that do not have a naturally reliable source of freshwater can live and run businesses in those areas. The project itself is made up of a network of aqueducts, dams, and other infrastructure designed to deliver water as well as generate electricity for California's electrical grid. [1] See Fig. 1 for a detailed map of the various sites that constitute the infrastructure, in addition to the population centers that benefit from its existence. Notably, the southern portion of the SWP serves to deliver water to customers in the City of Los Angeles (LA).
To fully understand the needs of LA in the context of water deliveries, one must understand the basic geophysical makeup of the LA Metropolitan Area. According to the Los Angeles Department of Water and Power (LADWP), 90% of water is received from sources outside of the area, meaning water imported through aqueducts either from the SWP or other projects designed to extract resources from more water rich areas of the United States. [2] In their annual report for the fiscal year 2021-2022, the department explains that merely 8% of the water for the city is extracted from aquifers that contain groundwater. Thus, one can conclude that this infrastructure exists for the transportation of water to a region that lacks a plentiful amount of it for its residents and businesses.
Officials with the DWR have warned about the "impacts of warming temperatures, shifting hydrology, and rising sea levels" on the infrastructure that allows the state and federal governments to redirect water resources through canals and aqueducts to customers such as LA, highlighting the effects of current and future droughts on the storage devices (reservoirs) used to export water. [3] This has led to efforts to reduce the amount of water being delivered, such as creating incentive programs or promoting alternatives to common uses of water, such as installing turf instead of planting grass. [2] Nevertheless, it may not be prudent to rely on water exports from regions that may not be able to make the same level of deliveries in the future, given the environmental changes occurring to the planet.
As an alternative to importing water from faraway places that may not be able to sustainably supply it for a long period of time, some coastal cities in California have proposed desalinating water from the ocean. The San Diego County Water Authority hired a firm to operate the Carlsbad Seawater Desalination Plant and reduce their dependence on water imports. [4] An environmental report prepared by leaders of the plant notes that there are significant energy costs associated with constructing and operating the infrastructure. As a thought exercise and preview of what may be the future of freshwater in the state of California, this webpage will outline the energy costs of providing 100% of the City of Los Angeles's water through a desalination plant.
This calculation uses data provided in the environmental report and LADWP's annual report. [2,4]
454 million gallons of water are consumed in the City of Los Angeles on a daily basis, equivalent to 1.718 × 106 m3. Thus, roughly 6.272 × 108 m3 are consumed annually. This is the amount of water that would need to be supplied by a hypothetical desalination plant.
The Carlsbad Seawater Desalination Plant supplies 50 million gallons of water a day, equivalent to 6.908 × 107 m3 annually. The electricity required to process this amount of water is 2.744 × 105 MWh per year. Equivalently, 9.878 × 1014 joules per year. Thus, each desalinated cubic meter of water requires 1.4301 × 107 joules.
Extrapolating these figures to LA's water usage, we can determine how much electricity a desalination plant would consume. This hypothetical plant would consume 8.97 × 1015 joules per year.
In order to understand the magnitude of this number, we can compare this energy usage to the amount of electricity that LADWP delivers to its customers annually, which is 7.501 × 1016 joules.
| 8.97 × 1015 J y-1 7.50 × 1016 J y-1 |
= | 0.12 |
This means that a desalination plant to cover the freshwater needs of LA customers would increase electricity consumption in the city by nearly 12%.
Considering that the production of desalinated water does not depend on drought conditions or other environmental factors that may impact access to imported water, a 12% increase in electricity usage is an attractive option to California water policy architects. Advocates for desalination are often on the defensive when it comes to justifying their energy usage and costs. [4] On the other hand, the SWP faces challenges that maybecome insurmountable due to the environmental conditions that the state will need to contend in the future. [3] These challenges, in addition to the fact that access to SWP water and related projects has been and will continue to be volatile, may push regional governments to take matters into their own hands.
The calculations performed here can be generally extrapolated to the population centers in the coastal regions of California that would benefit the most from desalination. This is because a city's electricity consumption is expected to be a function of population.
To conclude, imported water, the freshwater that coastal cities in California rely on to hydrate their populace, faces a problematic future. [1,3] Desalination has its critics, but as it becomes cheaper to produce electricity without relying on fossil fuels and technological advances are made to increase efficiencies, a transition to desalination may become inevitable.
© Caetano Melone. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "State Water Project Energy Roadmap," California Department of Water Resources, 2021.
[2] "2021-2022 Briefing Book," Los Angeles Department of Water and Power, 2022.
[3] J. Wang et al., "Mean and Extreme Climate Change Impacts on the State Water Project," California Department of Water Resources, CCCA4-2018-004, August 2018.
[4] "Energy Minimization and Greenhouse Gas Reduction Plan," Carlsbad Seawater Desalination Project, 10 Dec 08.
