Mexico City will have enough water for four decades

Water is extracted from the subsoil 40,000 liters per second, two-thirds of the total consumed in the metropolitan area. Every day we will depend more on subway sources. World Water Day is celebrated on March 22. We have to pump the resource from greater depths.

Mexico City will have enough water for four decades
Mexico City in the rain: World Water Day is celebrated on March 22. Photo by Alejandro / Unsplash

If we do not make drastic changes regarding the vital subway liquid, we will be heading towards a silent catastrophe, which is not as visible as when the level of the dams decreases, a river is contaminated or a spring dries up. "Here we cannot see with the same drama the disaster that is happening," says Manuel Perló Cohen, of UNAM's Institute of Social Research (IIS).

Mexico has 653 aquifers defined and 38.7 percent of this resource used in the country comes from these sources; of these, 105 are overexploited, that is, extraction exceeds recharge, in several of them by more than 100 percent. For example, the Valley of Mexico, the one called Texcoco, presents this situation in 800 percent.

The majority is where it rains less, from the center to the north of the territory, in entities such as Querétaro, San Luis Potosí, Durango, Zacatecas, Coahuila, Nuevo León, the North Pacific coast and the Baja California Peninsula.

In this region of the national territory, 40 thousand liters per second are extracted from the subsoil, which means two-thirds of the total consumed in the metropolitan area of Mexico City. Another important quantity is brought from the Cutzamala system (approximately 15,000 liters per second) and another from the Toluca-Lerma aquifer.

To supply the country's capital, the aquifers of the capital are overexploited as well as those of neighbors (State of Mexico and Hidalgo), some of which are 100 kilometers away. At the current rate of extraction, it is estimated that Mexico City would have enough water left for about 40 years.

Beneath one's feet lies a wealth that is greater than that of oil: extraordinary, generous aquifers that have served the entire nation, especially those areas where there is little rainfall, where there is no liquid available from surface sources. This is the most important treasure in terms of natural resources. Nothing can compare with what water represents and the shortages that would mean not having it. Imagine what it would be like to be without it for just one day.

Extraction vs. recharge

According to the National Water Commission, 60.8 percent of the vital liquid with consumptive use (i.e., agricultural, public supply, self-supplied industry, and thermoelectric plants) came, in 2018, from surface sources (rivers, streams, lakes, and dams), and the rest from groundwater.

Its largest consumption is agricultural, 75.7 percent, and its predominant origin is surface, with 63.4 percent. On the other hand, public supply, which includes all water delivered through drinking water networks, both to domestic users and industries and services, is based mainly on groundwater, with 56.7 percent of the volume.

Aquifers are found at different depths, ranging from tens to hundreds or thousands of meters. Their main recharge is rain and snow that infiltrate into the subsoil when they are absorbed by the earth's surface. Groundwater is extracted utilizing pumps and wells, although there are also outcrops in springs.

It must be said that knowledge in this area is deficient, the expert acknowledges. And he adds: "It is not easy to know how much water there is in the subsoil; very modern studies must be made, with very advanced technology to be able to identify how much resource there is and what quality it has, if it is drinkable or not, because many times it can contain chemical substances, naturally present". This is the case in places like the Iztapalapa district of Mexico City, where it is necessary to treat the water extracted from almost 80 wells.

The overexploitation of aquifers generates serious problems because the water reserves are depleted: "we have to pump the resource from greater depths each time, with the consequent increase in costs; and when the wells are depleted they have to be replaced, new ones have to be built".

It also causes subsidence of the subsoil, such as that of Mexico City's Zócalo, which today is eight meters below the level it was a century ago; furthermore, it breaks down infrastructure and causes difficulties with seawater intrusion into the subway freshwater reserves near the coasts, making it unfit for human consumption; this has recently happened in the city of La Paz, Baja California Sur, for example.

These problems are compounded by contamination, particularly in agricultural areas, due to the use of pesticides that also infiltrate the aquifer, and in cities due to the intrusion of drainage water into the water table. There are also transnational aquifers, which Mexico shares with the United States, as well as with Guatemala and Belize. However, there is a lack of international legislation or treaties to regulate their use; each nation has its policy and this could become a conflict in the future.

On the occasion of World Water Day, which is celebrated on March 22 and this year's theme is "Groundwater, making the invisible visible", the doctor in Urban-Regional Planning from the University of California, Berkeley, adds that we are going to depend more and more on this source every day.

This is related to the growth of cities in regions of the country where the liquid comes mainly from the groundwater table, and to the climate change scenario that will represent an increase in temperature and a decrease in rainfall, which will significantly affect surface water sources in those areas.

The celebration has been held since 1994. According to figures from the United Nations and the National Council for the Evaluation of Social Development Policy, 2.2 billion people live without access to drinking water. In Mexico, between 12.5 million and 15 million inhabitants (approximately 10 percent) do not have access to this resource; of these, 9.3 million do not have an outlet in their homes.

What to do?

Manuel Perló stresses that we can take various actions to stop the process of aquifer deterioration; "reversing it is a more serious and difficult thing, but at least we can slow it down so that the slope does not become increasingly acute and extreme".

More research is needed to know the level of water reserves. The scientific knowledge that is promoted in universities, such as UNAM, and the government, must be increased to know the amount of liquid the country has. Accurate data is needed to know how much is in the reserves, how much is infiltrated, extracted, consumed, etcetera.

Similarly, it is important to protect the aquifer recharge areas; they must be preserved as if they were sacred places because if they are lost, the water that should infiltrate will run through the asphalt and end up in the drainage system. Another option is to artificially recharge aquifers with quality treated water, as is done in countries such as the United States, Australia, Germany, and Israel.

Subway extraction must also be reduced through the efficient use and care of the vital liquid, with the help of energy-saving domestic and industrial consumption equipment. "In households, we have a great potential for savings, but there must also be a significant change in agricultural activity". We must rescue the aquifers, protect them and turn them into the guarantee of our future; our life depends on them, he concludes.