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| Fig. 1: View of water transfer pumps of an Australian desalination plant. (Source: Wikimedia Commons) |
On May 6th, 2015 California's State Water Resources Control Board, called the SWRCB, approved an amendment to the state's Water Quality Control Plan for the Ocean Waters of California to create a legal framework for the expansion of seawater desalination in the state. Desalination is the process by which saltwater is purified into drinkable water through the removal of dissolved minerals. This marked the first moment a U.S. state has adopted guidelines for desalination. This amendment was met with criticism over the negative impact on marine life and green house gas emissions from these desalination plants. [1] The plants themselves do not produce green house gases, however, they just require a large amount of energy to operate which, in turn, can cause upstream green house gas emissions.
This decision came during California's historic drought that depleted their freshwater supplies, sounding the alarm for long-term water solutions.
In 2008, UCLA Geography Professor Glen MacDonald raised the warning of a hypothetical "perfect drought", in which a prolonged drought affected Southern California, the Sacramento River basin, and the upper Colorado River basin simultaneously. Such droughts have occurred in the last century, but never for a prolonged period of 5 years or more. The last time such a "perfect drought" had occurred was in the mid-11th and mid-12th centuries during the "Medieval Climate Anomaly". [2] In 2014, low precipitation levels combined with high temperatures resulted in a record-breaking Palmer Drought Severity Index. [3]
Southern California, the area stretching from San Diego to Los Angeles, consumes 10,000,000 acre-feet of water annually. The State Water Project pipes some 2.3 million acre-feet of water from the Sacramento River southward each year to help supply Southern California urban users. Another 4.4 million acre-feet is derived from the further Colorado River system. This totals to 70% of Southern California's water usage being met by extra-regional sources, mainly northern California and the Sacramento River system and the upper basin region of the Colorado River system. [2]
Previously, droughts have been combated by tapping into the large, deep groundwater resources of California. Over the past 150 years, the water usage during these periodic droughts far eclipsed the groundwater available from local precipitation. This has encouraged water mining, which drills to deeper freshwater, in turn lowering the water table. [2]
The Colorado River is the largest single source of water for Southern California. The State of California is allotted 4.4 million acre-feet from the river, being the largest share. The Colorado River has similarly been affected by the warming climate, putting its largest reservoir, Lake Mead, at low capacities. As of this writing, Lake Mead's water level has dropped further than in the 2014 "perfect drought" to 1,043 feet above sealevel, or 27% of its capacity. [3]
The drought that struck California in 2014 was this "perfect drought", exacerbated by record-breaking high temperatures. More and more "perfect droughts" likely lay in California's future. As ground water supplies further decrease and warming temperatures accompany future droughts, the need for more reliable solutions is evident. Water Desalination can be used to supplement California's water needs, but at a price. The large amounts of energy involved in water desalination will drive up the cost of water and cause upstream effects of energy generation. The amount of energy needed to supplement California's water supply is calculable.
Seven months after the SWRCB amendment to the state's Water Quality Control Plan, the largest seawater desalination plant in the Western Hemisphere opened: The Carlsbad Seawater Desalination Plant. This plant produces around 50,000,000 gallons, or 1.89 × 105 m3, of water per day. [1] Currently, water desalination takes 7 to 30 kWh of energy per 1000 gallons of desalinated water. Converting that into SI units, it is between 1.85 kWh m-3 and 7.93 kWh m-3. [4] This means, at peak capacity, the daily Carlsbad Seawater Desalination Plant energy consumption is:
| High Estimate: | 7.93 kWh m-3 × 1.89 × 105 m3 day-1 | = 1.50 × 106 kWh day-1 | = 6.24 × 107 W |
| Low Estimate: | 1.85 kWh m-3 × 1.89 × 105 m3 day-1 | = 3.50 × 105 kWh day-1 | = 1.46 × 107 W |
The process of purifying the water can be costly. The levelized cost of water takes into account the capital costs, operating costs, and financial costs of the desalination plant amortized over its output of desalinated water. The timeline for these costs is on the magnitude of multiple decades. The levelized cost of water at Carlsbad Seawater Desalination Plant is $1.84 m-3. [5] At peak capacity, the water produced by Carlsbad costs almost $350,000 daily.
Desalination plants exist all of the globe, with a high concentration in the Middle East and Australia, shown in Fig. 1. More than 15 other water desalination plants are in planning or construction in California, most of which are smaller than Carlsbad. [1] As the capacity of California's desalination infrastructure increases combined with worsening droughts, so will its reliance on desaliated water. As stated earlier, Southern California consumes 10,000,000 acre-feet, or 1.23 × 1010 m3, of freshwater per year. Table 1 shows the energy consumption and cost of operation for multiple desalination plants operating similar to Carlsbad at varying degrees of Southern California water dependence. For the energy consumed, a mean estimate of 4.89 kWh m-3 is used.
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| Table 1: Energy Required, Cost of Water, and Carlsbad-like plants needed per year for varying degrees of desalination dependence of Southern California freshwater. |
As the drought situation in California continues to exacerbate, the need for more long-term solutions grows. While desalination provides a more reliable resource of freshwater, it comes at a high price. If the 70% of Southern California's freshwater consumption that is sourced extra-regionally is replaced by desalination, it would require 125 desalination plants identical to Carlsbad. Carlsbad Seawater Desalination Plant is the largest such plant in the Western Hemisphere and cost $1 billion to build. [1] There's work being done to make desalination plants more efficient, like pairing them with nuclear power plants and using the salinated runoff as coolant water for the power plant. [5] Yet there are still other ways to adapt to the drought crisis. The freshwater need can be lowered at the household level through changing landscaping practices to use low-water plants and at the industrial level through better agricultural practices. [2]
© Dominic Terrones. 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] T. Denson, "Desalination and California's Water Problem", Georget. Environ. Law Rev. 28, 713 (2016).
[2] G. M. MacDonald, K.V. Kremenstski, and H.Hidalgo, "Southern California and the Perfect Drought," Quat. Int. 188, 11 (2012).
[3] "Lower Colorado River Supply Report," U.S. Bureau of Reclamation, 12 Dec 22.
[4] S. V. Veerapaneni et al., "Reducing Energy Consumption for Seawater Desalination," J. Am. Water Works Assoc. 99, 95 (2007).
[5] A. T. Bouma et al., "Energy and Water Without Carbon: Integrated Deslination and Nuclear Power at Diablo Canyon," Appl. Energy 323, 119612 (2022).
