California farmers have a water crisis. Not enough of the stuff and the supply keeps shrinking. The coastal urban dwellers aren’t all that sympathetic. A common sentiment: they shouldn’t be growing crops that need so much water, not in such a drought-prone state. Tear up those almond orchards!

Thing is, California farms are among the most productive in the world, meaning they require less land to produce more crop. Per the US Geological Survey, California’s Central Valley supplies 8% of US agricultural output (by value) on less than 1% of US farmland and produces 1/4 of the nation's food, including 40% of the nation's fruits, nuts, and other table foods. If California farmers closed up shop, land would need to be cleared somewhere else to grow their crops, at the expense of wild habitat. And more land would have to be cleared elsewhere than farmland abandoned in California, because the state’s farmland is so productive. So let’s keep the almond trees in California and figure out a way to access more water for all those crops.

Lots could be done to sustainably increase water supply in drought-prone regions like California, including*:

  • Enhanced conservation and efficiency

  • Water reuse, especially potable reuse

  • Stormwater capture for water supply

  • Water banking/aquifer recharge

  • Desalination, both brackish water and seawater

This rest of this post will focus on seawater desalination, because seawater is an unlimited resource (at least in this geologic age) and desalination technology is evolving. Unfortunately, desalination plants still have a reputation for being expensive energy-hogs that inflict considerable environmental harm. Per the Santa Clara Valley Water District, here’s a brief explanation of the problems:

Environment: To desalinate water, the water first must be transferred from an ocean or brackish water source to the desalination plant. Once it is filtered, the treated water is moved through the water delivery system while the salts, solids and other matter, known as brine, that have been filtered out of the water must be properly managed. The intake process and disposal of brine pose environmental challenges. Drawing water into a plant, depending on where and how it is done, can threaten marine life. Special precautions are necessary to avoid trapping and killing sea life. Special precautions are also necessary when disposing of the highly saline brine. If it is returned to the sea or bay, it needs to be done so carefully, so the super-salty water does not harm marine life.

Energy: The energy required in the desalination treatment process is also a major challenge. Filtering the salts and other compounds from sea water must be done at very high pressure, which requires a significant amount of energy. The impact to our carbon footprint must be considered in any proposal to develop a desalination plant.

And now the good news: the cost of desalination has dropped by over half over the last three decades (Robbins, 2019). Desalination still isn’t cheap but it is increasingly affordable - especially in developed countries. For example, a desalination plant in Israel can produce around 260 gallons of drinking water for less than one US dollar (Jacobsen, 2016).

Plus, the amount of energy required for desalination has fallen significantly since the 1990s. Even better, desalination plants are expected to transition to renewable sources of energy over the next few decades, with the potential to become fully decarbonized later this century (Pistocchi,. Bleninger, et al., 2020).

The remaining challenge is environmental, specifically the impact of brine disposal on marine ecosystems. As with the other challenges, progress has been made. Brine and other pollutants can be diluted, treated, or deposited well offshore for quick dispersal. These methods reduce environmental harm, sometimes to the point of no measurable impact. More can be done, but to quote a recent paper on desalination, “Brine disposal is a manageable issue” (Pistocchi,. Bleninger, et al., 2020).

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* List care of Luthy, Wolfand, et al (2020). Complete reference below.

References:

As Water Scarcity Increases, Desalination Plants Are on the Rise. Jim Robbins/e360.yale.edu June 11, 2019

Israel Proves the Desalination Era Is Here: One of the driest countries on Earth now makes more freshwater than it needs. By Rowan Jacobsen/ Scientific American. July 29, 2016

Luthy, R. G., J. M. Wolfand, et al. (2020). "Urban Water Revolution: Sustainable Water Futures for California Cities." Journal of Environmental Engineering 146(7): 04020065. https://ascelibrary.org/doi/10.1061/%28ASCE%29EE.1943-7870.0001715

Pistocchi, A., T. Bleninger, et al. (2020). "Can seawater desalination be a win-win fix to our water cycle?" Water Research 182: 115906. https://doi.org/10.1016/j.watres.2020.115906