Water Challenges Facing Mexico City

The focus of this paper is to report on the strategy of Manuel Frías, a renowned engineer from the National Polytechnic Institute of Mexico (IPN), to improve and alleviate the water scarcity of Mexico City using geothermal energy of the Popocatepetl volcano.

Mexico City, one of the largest city in the world is facing a severe water “crisis.” Its troubled relationship with water dates back approximately 700 years. Legend has it that when the Aztecs were still nomads they were looking for a place to settle down. The Gods would signal them to the right place. They found there special sign on the middle of the lake, so they built their city there; on the lake. They accomplished such a feat by making these artificial floating islands called chinampas. They would stuff mats with mud from the lakebed and fix them to the bottom with tree trunks that would later sprout to trees with roots. Apparently, a city made out of floating islands was quite a site, even by modern architectural standards.

When the Spanish conquistadores took over 200 years later, they built a new city on top, and it has kept growing over the years. The lakes dried out, everything replaced by a great mass of concrete. Today, only in some Southern neighborhoods of the city, there are still some remains of what the floating city was once like. Claudia Medina’s ancestors used to work the lands made by these chinampas in Xochimilco. “The water we used to have here, many years ago, was spring water. My grandparents used to say that when they were thirsty they’d simply drink water from the canals, because water was crystal clear and beautiful. But when the water demand for water increased, they routed all the springs through culverts. And to prevent the canals from drying out, they supplied them with water from treatment plants from the city and surrounding areas. In theory, the treated water’s quality is good for agriculture. But we’d have to carry out an analysis to check if it’s really the case,” says Medina, a biologist and chinampa owner.

After drying everything out, the bulk of the city rests on the muddy soils of the lakebeds causing many problems. For one, when seismic waves enter the region, the soft sediments act as an amplifier, making earthquakes like the ones on September 19, 2017 even more devastating. Similarly, the city is sinking over the soft ground, and that is also connected with water. The water supply of Mexico City is aggravated by over-exploitation of the aquifer. It has been calculated that only 50% of water extracted returns to the aquifer, which severely comprises the city’s soil causing the entire city to sink unevenly at a rate of 25 mm a month. Buildings distort and water pipes break. Almost 40% of the water is lost in leaks because of this. Then getting dirty water out of the city is another feat of modern engineering, it has to be pumped out through another lengthy system of pumps. Both the pumping in and out of water require huge amounts of energy and lots of money, and yet there is still not enough water for the 21.2 million people living in the valley. Approximately 70% of Mexico City’s inhabitants receive tap water for a few hours a day, others on a weekly basis. Take Xochimilco (Mexico City municipality) for example, people there are lucky if they receive water on their tap for a couple of hours a week. They rely on trucks that carry the water from the local wells to their storage tanks. The tanks that are visible outside houses on every stretch of the neighborhood. Others use animals for the task. Moises Martinez, a Xochimilco resident, says his home is not even connected to the water grid. This deficit in water availability in Mexico City, together with the complexity of its population and of the diversity of hydraulic infrastructure, leads to an unequal distribution of water, leaving the poor population in a situation of exclusion, which aggravates its vulnerability to health risks. In some marginal areas of the city, per capita consumption is between 19 and 24 liters per day, in periods of more or less regular supply by trucks. This consumption is reduced to a minimum of four liters per day in the rainy season, when road conditions hamper this service.

In the light of this dependence on the local aquifer and on neighboring basins, the city faces a paradox. It is estimated that the basin of Mexico City receives an estimated rainfall of 210 m3/s, the proper management of which would meet the demand of population and of the different activities of the capital, as well as prevent regular flooding. The National Water Commission of Mexico estimates that the average annual precipitation is about 7 billion m3, corresponding to 222 m3/s, of which 80% evaporates, 11% filters into the soil, and 9% is surface runoff.

However, rainwater runoff is mixed with sewage, a situation which has been heightened with the development of the aquifer’s recharge zones. In addition to this, the water losses caused by poor hydraulic infrastructure conditions are greater than one-third of supply. On the other hand, only 3% of the sewage is treated, which is insufficient for even 5% of the city’s demand for water. At the beginning of the 20th century, 60% of the water supply was obtained from surface water and the rest from wells in the Valley of Mexico. Today only 2% is surface water, while 68% is from the aquifer, and 30% is supplied by the Cutzamala system — an exemplary feat of hydraulic engineering that transports water, from neighboring river basins, over a distance of 127 km and pumped for a thousand meters uphill, like its gravity, to the Valley of Mexico.

The impressive population growth of Mexico City in the twentieth century was due to multiple causes. In the first place, the concentration of economic activities in the capital of the country attracted important flows of population, mainly people of rural origin, who were incorporated into the newly born and pungent or intense industrial activity which offered attractive salaries, together with urban services appropriate for a city in expansion. In fact, the education, medical, and health services which were offered to the growing number of inhabitants, together with the access to better quality food and housing, all contributed to reduce the incidence of infectious diseases, which until a few decades previously were the main cause of death, thus diminishing the high death rates, especially among children. According to the official projections on behalf of the National Population Council, it was estimated that the population of Mexico City would reach a total of 20 million inhabitants, by the year 2010. Previous estimates had projected that figure for 1995, indicating that Mexico City was on course to be the largest city on the planet; the decrease in fertility, but above all the diminished immigration, caused these figures to decline during the last decades of the twentieth century.

Mexico City is considered one of the largest cities in the world, and is home to 20% of Mexico's entire population, making Mexico City the most populous metropolitan area in the Western Hemisphere. The World Population Review estimates that the city’s population will reach 22 million by the year 2020. This deficit in water availability in Mexico City, together with the complexity of its population and of the diversity of hydraulic infrastructure, leads to an unequal distribution of water, leaving the poor population in a situation of exclusion, which aggravates its vulnerability to health risks. In some marginal areas of the city, per capita consumption is between 19 and 24 liters per day, in periods of more or less regular supply by trucks. This consumption is reduced to a minimum of four liters per day in the rainy season, when road conditions hamper this service.