By Emilio Godoy
MEXICO CITY, Jan 31 2021 – Mexico is seeking to mitigate water shortages in part of its extensive territory by resorting to seawater, through the expansion of desalination plants. But this solution has exorbitant costs and significant environmental impacts.
Among the advantages of these water treatment plants, Gabriela Muñoz, a researcher at the public university El Colegio de la Frontera Norte, highlighted the expansion of water sources and the production of water for human consumption.
But in her conversation with IPS, she also underlined the disadvantages of these plants, such as high energy requirements, aggravated if the energy comes from fossil sources; high costs; and the generation of brine and wastewater.”Before considering desalination, measures such as water saving, investment in green infrastructure, rainwater harvesting and the reuse of treated water should be a priority. We must also compare the costs of building desalination plants versus alternatives.” — Gabriela Muñoz
To illustrate the costs: one of the desalination plants authorised in 2014 by the National Water Commission (CONAGUA) in the northern state of Baja California cost some 35 million dollars to process 250 litres per second (l/s). Another plant with the same capacity, given final approval in October 2020 in the neighbouring state of Baja California Sur, will require an investment of more than 55 million dollars.
In Mexico “there are no regulations regarding how to dispose of the brine. The most common thing to do is to dump it on the beach. We have to be careful how we handle the brine because of the toxicity to ecosystems. Nor is there installed capacity to treat all the wastewater. For specific areas, desalination should not be the first option,” said Muñoz from the northern border city of Tijuana.
Between 2012 and 2020, environmental authorities authorised at least 120 desalination facilities, rejected six applications and another five are under evaluation, according to data obtained by IPS through public information requests. Most of the new projects are located in three states with acute water shortages: the northwestern states of Baja California and Baja California Sur, and the southeastern state of Quintana Roo.
However, in Mexico, where more than 400 such plants operate, there has been no research on their ecological effects, as corroborated by IPS, with the exception of the study “Desalination of water”, published in 2000 by the government’s Mexican Water Institute.
One basic desalination technique is thermal distillation, in which seawater is heated until it evaporates, the vapor condenses to form freshwater, and the remaining liquid is discarded as concentrated brine.
Another is reverse osmosis, in which water is filtered and then pumped at high pressure through thin membranes that only allow the liquid to pass through and retain the salt.
In 2019, the study “The State of Desalination and Brine Production: A Global Outlook”, produced by the United Nations University Institute for Water, Environment and Health, based in Ontario, Canada, warned of the growing generation of brine and its serious effects on the environment. The process of extracting brine, it estimated, accumulated a total of 142 million cubic metres (m3) of waste worldwide that year.
There are 18,214 desalination plants around the world, with an installed capacity of 89 million m3 per day, serving more than 300 million people, according to the latest data from the International Desalination Association. For every litre of water desalinated, a litre of brine is produced.
These plants are part of a trend towards the introduction of this technology in areas facing the threat of water stress or scarcity.
Water availability in Mexico
Mexico, Latin America’s second largest economy, has an area of 1.96 million square kilometres, 67 percent of which is arid and semi-arid land.
According to CONAGUA, water availability varies widely in this country of 129 million people, as it is scarce in the north and abundant in the south.
Of every 100 litres of rainfall, 72 return to the atmosphere through evapotranspiration, 22 run off into rivers and streams, and six feed 653 aquifers, of which 108 were overexploited, 32 had saline soils or brackish water, and 18 had seawater infiltration due to rising sea levels and seepage into the water table.
Although Mexico had a low national water stress level in 2017 – 19.5 percent – its risk of water stress is high, according to the Aqueduct platform, developed by the Aqueduct Alliance, made up of governments, companies and foundations.
In fact, Mexico is the second most water-stressed country in the Americas, after Chile. Water stress could be a problem by 2040 from the centre to the north of the country.
Meanwhile, the extreme northwest presents a medium-high risk of aquifer depletion and practically the entire Gulf of Mexico and the Caribbean Sea present a medium-high risk of drought, precisely where most of the desalination plants are located.
Aqueduct takes into account 13 indicators of water stress, such as groundwater availability and depletion.
In the last five months, drought has worsened in Mexico – the third worst record of the century – a consequence of the climate crisis, according to data from the National Meteorological Service.
In Mexico water use is intense, reflected in its water footprint – the impact of human activities on water – of 1,978 m3/person per year, compared to a global average of 1,385.
As a result, national and regional authorities have set their sights on seawater, given that Mexico is bordered by the Pacific Ocean to the west and the Atlantic Ocean to the east, and there are a total of 150 municipalities with a coastline, out of a total of 2,466, according to the National Policy on Mexico’s Seas and Coasts.
This year, Héctor Aviña, an academic at the Engineering Research Institute of the National Autonomous University of Mexico, plans to scale up his prototype geothermal-powered desalination plant in the city of Los Cabos, located in Baja California Sur, some 1,650 kilometres northwest of Mexico City.
“I don’t know if it is the best option because of brine generation and well exploitation, but it is a good alternative. Many areas are already experiencing water stress. In those places, desalination and beach wells can help aquifers recover,” Aviña told IPS from Mexico City.
The 500,000 dollar plan consists of upgrading a pilot plant from the current capacity of four m3 per day to 40 m3 and, if possible, to 400 m3, in an initiative to be developed with the state-owned Mexican Centre for Innovation in Geothermal Energy.
The project will take advantage of nearby hot water wells to obtain water and geothermal energy.
With this technology, the cost per m3 of water ranges from 0.8 to 1.3 dollars, compared to 0.6 to 1.00 dollars using reverse osmosis.
The National Infrastructure Investment Agreement, signed between the federal government and members of the business community in November 2020, includes the foundations for four desalination plants in Baja California, Baja California Sur and Sonora, with an investment of 643 million dollars and a capacity of 650 l/s.
But Muñoz suggested that before turning to desalination, poor irrigation practices, leaks and aging infrastructure should be addressed.
“Before considering desalination, measures such as water saving, investment in green infrastructure, rainwater harvesting and the reuse of treated water should be a priority. We must also compare the costs of building desalination plants versus alternatives,” she said.
In 2014 Aviña designed a reverse osmosis model equipped with solar panels and batteries, which has competitive costs.
“In other areas, the source of energy must be reviewed. Mexico is going to have water problems, it is a situation that we will have to live with. If we study it well, if we manage it well, desalination is a good alternative,” he argued.