Water Desalination: Savior, Devil, or Just Average?

Water scarcity is a fact of life in New Mexico, the American Southwest, and much of the world as a whole. With a growing population and improving standards of living, water demand has only increased over time, at the same time as rainfall is decreasing and evaporation increasing in many arid regions due to climate change. In almost every single case, the largest user of water by far is agriculture, but huge amounts are also used by industries like power generation and mining, as well as private homes and commercial areas. There are many ways to reduce water use in these sectors, but they either cost a lot of money or lead to lower outputs. So, it’s easy to see why the idea of making currently useless salty water useful would be attractive. But is it actually a good idea?

First off, how does desalination work? There are several ways to separate water from dissolved salts. The oldest of these is distillation, but this is extremely energy inefficient and barely used anymore. Far more common nowadays is reverse osmosis, which works by squeezing the water solution through a membrane with extremely small pores that will let water through, but not larger molecules. This includes not only large organic molecules but also charged ions, since the charge creates a spherical “solvation cage” of bound water molecules around it that makes even small ions like sodium act like much larger molecules than the sodium atom itself. This is more energy efficient, with reverse osmosis requiring 4-16 kWh of electricity ($0.6-2.4) per thousand gallons of water depending on the salinity of the water and quality of the membrane. This isn’t the only cost, since membranes, pumps, wells for both production and waste injection, and other equipment is needed. Issues include the fact that, small, uncharged pollutants will go right through the membrane, the presence of dissolved limestone or gypsum in the water can cause scaling that will destroy the membrane, and all of the salts and other dissolved pollutants are still dissolved in a more concentrated waste brine stream that is produced alongside the fresh water. None of these challenges are necessarily deal breaking in themselves, but they need to be kept in mind.

This might be great if you’re by the ocean, but how is this relevant to New Mexico? New Mexico actually has several dozen aquifers with water of different salinity levels, many of which are much lower than seawater while still being too salty to use for irrigation untreated. For example, groundwater from the Las Vegas basin has an average total dissolved solids content of 2.3 grams per liter, too high for most crops but 15 times lower than that of seawater (35 grams per liter). This means that desalinating it would use much less energy and produce much less waste brine than desalinating the same amount of seawater. Getting rid of the waste brine is still a problem, but for fairly low salinity aquifers like that you can just reinject it into the aquifer if you’re ok with it becoming more salty over time without too much of an issue. Still, groundwater has issues that ocean water doesn’t have. Firstly, these aquifers contain enough water to meet centuries of current water use if all of it was desalinated, but it is still a finite source that could eventually run out. Groundwater in places like the San Juan and Albuquerque basins often contain high amounts of arsenic and/or uranium, which makes the brine significantly more hazardous. Also, arsenic in groundwater is not efficiently removed by reverse osmosis, unlike arsenic in surface waters. This is because arsenic in reduced (oxygen-free) environments like underground aquifers is in the arsenite form, which is neutral (uncharged) at normal pH values. However, in the presence of oxygen, arsenic is more stable in the arsenate form, which is negatively charged at all but extremely acidic pH values. Since arsenite is neutral, there is no solvation cage of bound water molecules around it, letting it easily pass through many reverse osmosis membranes. This can be solved by bubbling air through the groundwater and letting it react for several days before putting it through the reverse osmosis process, but this makes it more expensive and also just shifts the arsenic to the waste brine stream that still needs to be dealt with. Small organic molecules from oil or natural gas, including carcinogens like benzene and its derivatives, are also small enough that at least some will make it through the pores of most membranes, and require more expensive treatments like ozonation to remove.

Water desalination has become a controversial issue in some regions, with few people on either side seemingly having any idea what they’re talking about. Some people have gone completely onboard the desalination bandwagon, saying that it should be used to make drinking water from highly contaminated sources like produced water from fracking despite the fact that it will have issues removing several of the likely contaminants. Many of its strong proponents also use it as a way to completely ignore possible ways of reducing water use that might be cheaper than pumping up and treating huge amounts of salty groundwater just to waste it. Government- funded water desalination could also just end up subsidizing wasteful water use by large farmers and other companies with the taxes of working people, instead of requiring these companies to invest in water efficiency using their own money. For example, Democratic candidate for governor Sam Bregman is extremely pro brackish water development, even of contaminated sources like produced water, and repeats extremely optimistic estimates of New Mexico’s brackish water reserves while ignoring possible issues like contaminants making it through reverse osmosis membranes without additional treatment. Several oil producer associations are also very pro-produced water reuse, again ignoring the possible risks and added costs.

The fact that the proponents of water desalination completely ignore all evidence against their side doesn’t mean the opponents are any more balanced. For example, the environmental group New Energy Economy NM wrote an article that was completely against all water desalination, saying that even brackish water from essentially harmless systems like the Las Vegas Aquifer are just as much of a threat as produced water contaminated with oil and other pollutants even though they objectively aren’t. They also stated that several substances like acetone (which is naturally produced on huge levels by fermentation of organic waste and even ketosis in humans and animals) or bromide (brominated vegetable oil is a common ingredient in sodas) are hazardous when they aren’t.

This extreme and uninformed opposition to desalination even extends to people within the DSA. For Corpus Christi DSA, the first page under their “Our Work” section is Ecosocialism, which is essentially only about their opposition to a proposed desalination plant. Corpus Christi is in the middle of a severe water crisis, with many nearby reservoirs being nearly empty. Most of the city’s water goes to six oil refineries and major petrochemical factories in the area, and these companies pay a much lower rate than the city’s residents for water. Due to the water shortage, the city government tried to get funding for a municipally owned water desalination plant to solve the crisis. Corpus Christi DSA, alongside several other progressive organizations, played a big part in getting the city to not fund it. Instead, Chevron is just building its own private water desalination plant, something no socialist or even social-democrat should describe as a win. If it was owned by the city, it could have been paid for by higher taxes on these oil companies, who could have been charged a high rate for this water while residents got it for cheap. They also spend far more time opposing this relatively harmless desalination plant than they do opposing the multiple active oil refineries and plastic factories, that release far more harmful pollutants than salty water, and are both the acute (due to their large water use) and long-term (due to their greenhouse gas emissions) cause of the water shortage that is making the desalination plant necessary in the first place. They also have factually incorrect information on their page, such as that brine from seawater (which contains minimal heavy metals) is “a cocktail of … heavy metals”. This is causing the Corpus Christi chapter to spend its time and resources opposing a fairly benign desalination plant, instead of opposing the oil refineries and plastic factories in their town, or maybe even helping workers unionize and actually pushing for socialism. Even when they partially achieved their goals by stopping a city-owned desalination plant, this only made the water crisis worse for Corpus Christi residents and weakened the city’s economic power. Furthermore, their complete inaction has made it so that the only ones actually helping people affected by the water crisis are the Republicans and oil companies, making them look better than the left. The Corpus Christi DSA, instead of making any detailed plans to deal with the water crisis by using water more efficiently instead of building a desalination plant, has instead just chosen to criticize the only solution that anyone in the area seems to be pursuing with no alternatives of their own. This is despite the fact that other alternatives, such as paying farmers to use more efficient irrigation methods that use less water, would be both cheaper and more environmentally friendly than a desalination plant.

Are there any alternatives to desalination in these situations? First, we need to establish what the main water users are. In the city of Corpus Christi, the massive petrochemical complexes are the main consumer, but when you go to New Mexico or America as a whole, the largest user by far is agriculture. According to this 2020 report by the Office of the State Engineer, the total water use of the state was 3.805 million acre-feet (1.24 trillion gallons), of which 1.923 million were groundwater and 1.882 million were surface water. Irrigated agriculture alone made up 78.0% of total water use in the state, at 2.967 million acre feet or 967 billion gallons per year. The main irrigated crops in the state are alfalfa, corn, pecans, and winter wheat, all of which besides pecans are mainly for animal feed. The entire public water supply, including the vast majority of homes and businesses in the state, only uses 7.9% of the state’s water. Other commercial users used 1.5% of the state’s water, industrial and mining users used 1.7%, and power generating stations used another 1.7%. Lastly, drinking water for livestock was 1.0% of the total, and private home wells were 0.8%. New developments might have added some more consumption, but not much compared to existing agriculture. For example, the planned Project Jupiter data center will use approximately 1,100 acre-feet or 360 million gallons of water a year. This is certainly a lot of water, but it’s less than 0.03% of New Mexico’s current water consumption. Even drinking water for livestock is almost nothing in comparison to the amount used to grow irrigated crops. So, if we want to make existing water supplies stretch further, the main target should be irrigated agriculture if we want to make a real difference.

Since irrigation uses more than three-quarters of the state’s water, we should look at it more closely. There are three main types of irrigation: flood, sprinkler, and drip. Flood irrigation is the oldest, and works by flooding the field for a period of time. This is simple and cheap to set up, but also the least efficient since much of the water will run off or evaporate. Sprinkler irrigation is the most common today, and is in between flood and drip irrigation in terms of both cost and efficiency. Drip irrigation is the newest and most efficient, and works by dripping water out of a buried tube directly into the root zone of the crops. In terms of efficiency, around 50% of applied water will actually be used by the plants with flood irrigation, 60-75% with sprinkler irrigation, and 90-95% with drip irrigation. Currently, according to the same state report used earlier, 63% of irrigated land in New Mexico uses sprinkler irrigation, 35% uses flood irrigation, and only 2% use drip irrigation. So, assuming efficiencies of 50%, 70%, and 90% of each type of irrigation, having all irrigated farms in the state switch to drip irrigation would change irrigation water use efficiency from 63.4% to 90%, reducing irrigation water use by 29.6% (878,000 acre-feet) or 23.1% of the state’s total. According to the USDA, there are currently around 600,000 acres of irrigated farmland in New Mexico. At a cost of $2500 per acre, switching the entire state over to drip irrigation would cost 1.5 billion dollars. For comparison, this proposal for California would make desalinated water with a startup cost of around $18,750 per acre-foot per year, or $16.5 billion for the same amount of water that would be saved by drip irrigation. So, in many cases, saving water with more efficient irrigation methods would be ten times cheaper than producing that much water with desalination, just to waste it.

There is also the option of using entirely different crops that require much less irrigation. Around 80% of New Mexico, over 60 million acres, is semi-arid rangeland that is basically only useful for low-intensity grazing. Typical values for rangeland productivity are 550 to 650 pounds or 0.3 tons of forage per acre per year, much of which is low-quality brush. When irrigated, this can produce 6-9 tons of corn forage (of which 30-50% or 2-4.5 tons is grain), 7-10 tons per acre for alfalfa, or 5 tons per acre for soybeans (of which 40-50% or 2-2.5 tons is grain). But, these require large amounts of water during the growing season, from 24 to 28 inches for corn, 20 to 26 inches for soybeans, or 18 to 36 inches for alfalfa. Tepary beans, on the other hand, can grow with as little as 2 to 5 inches of water over the growing season (July-October), enough that they could be grown without irrigation even in dry areas like Albuquerque. Wild varieties of these grow in much of New Mexico, and they have been cultivated by several different Indigenous groups in the southwestern US and northern Mexico for thousands of years. They haven’t been selectively bred as much as some other kinds of beans, and the seed yield under dryland conditions is approximately 600-700 pounds per acre. Assuming that, like other beans, the plant is about half grain by weight when harvested, this equals a total forage yield of around 0.7 tons per acre, of which 0.3 tons are beans. With the much lower yield, you can see why other types of bean are more common in wetter areas like the eastern US. Still, this is double the total amount of plant mass as unmanaged rangeland in New Mexico, and is also much higher nutritional quality than creosote bush or sage. Even if the yield per acre is ten times lower than alfalfa or corn, there are tens of millions of acres of land in our state suitable for growing tepary beans with no irrigation, as compared to the 0.6 million acres of irrigated farmland we have now that are already squeezing the rest of us dry. Also, not much work has been done on improving the yield of tepary beans using modern selective breeding and crossbreeding techniques, or measuring its response to different fertilizers. Texas A&M University started a project in 2022 to better characterize tepary beans as a crop for large-scale commercial production, but this is expected to take at least five years and the results have not been released yet.

The reverse osmosis technology used for water desalination also has numerous other uses. For example, some water currently used for drinking, watering livestock, and irrigating crops contains high amounts of heavy metals like arsenic and uranium. This can be removed fairly easily with reverse osmosis (as long as the arsenic is oxidized first), needing much lower pressures than more saline solutions. Since many people with contaminated water live in poor areas like the Navajo Nation or Mora, they are much less able to pay for treating their water than huge oil companies, and if anyone should be getting more funding for water treatment it’s them. Dealing with waste streams is also an issue that needs to be dealt with. Some common minerals, like iron oxides and hydroxides, will absorb both uranium and arsenic from solutions. Injecting waste streams containing low amounts of naturally present heavy metals into rock formations containing these minerals could be a way to permanently remove these contaminants from the water cycle. However, other studies show that not all iron oxyhydroxides efficiently absorb uranium, so we need more research before trying solutions like these on a large scale.

In conclusion, we need to understand the choice of water desalination in context. People should know both the potential benefits and issues, especially in comparison to methods of using the water we already have more efficiently. However, instead of just talking about how horrible desalination is, it would be better to talk about other ways to deal with the water crisis like using more water-efficient irrigation or different crops, instead of just saying that desalination is bad with no other alternatives. We should also put desalination in context compared to far more polluting industries like oil refineries, and seriously consider what areas we should focus our limited resources on.

The views expressed in this piece are those of the author and not necessarily those of The Red Rose, any individual editor, Albuquerque DSA, the Democratic Socialists of America, or any individual therein.

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