The rain harvesters of Mexico City

• The correspondent's look: Mexico City, the thirsty capital

Legend has it that the Aztecs decided to settle in the valley of Mexico guided by a prophecy. Upon arrival, they found a large lake presided over by an islet where, on top of a cactus, there was an eagle eating a snake; This signal, represented today in the Mexican flag, implied that they would cease to be wandering to establish at that point the epicenter of their Empire. Over the years, the Aztecs were expanding the size of their small island by throwing land on the lake. The repetition of this operation for more than 500 years takes us to the present-day Mexico City, a megalopolis built on a lake (of which there is hardly any vestige) and where about 22 million people live. The paradox in this city is evident: a city characterized by the abundance of water, where more rain falls annually than in London and, where, however, the possibility of running out of the vital liquid comes closer and closer.

Experts warn that the dreaded 'D' day, when the running water stops coming out of the taps, will arrive if the current dynamic is not reversed, in 2030. Among the main causes are the overexploitation of aquifers, the poor state of the pipes (it is estimated that they lose 40% of the water they carry), excess consumption and poor use of rainwater. In the most affluent areas of the Mexican capital, the warnings of the experts sound still unbelievable, but in their most popular neighborhoods, such as Iztapalapa, they know well enough what it means to live without running water. In these communities, the faucets only spit water for once every 7 days , forcing their tenants to accumulate everything they can to survive the rest of the week. However, this painful situation seems destined to change in the coming years thanks to the 'Rainwater harvest' program, financed by the new capital government.

The objective is to install, over the next 5 years, 100,000 rainwater collection systems in the most needy regions of the city. The design and installation is carried out by 'Isla Urbana', whose founder, Enrique Lomnitz, receives EL MUNDO at the doors of the warehouse from which he assumes that every day: "we are installing an average of 55 systems". Today it's the turn of Guadalupe, who, after 3 months of waiting, will officially become a 'rain harvester'.

To get to your home, located in what looks like the end of an infinite city, you have to climb a hillside populated by colorful houses and half-paved roads. 28 years ago, when Guadalupe moved to the top of Iztapalapa, she remembers that "there were barely 5 houses", and she regrets that overpopulation has affected so much the quality of life in her neighborhood: "People build as they want, they don't leave free space for the water to run, nor for green areas. " Here, every time it rains, the highest streets become dangerous torrents of water that "drag everything down, until the hermitage is flooded," Guadalupe confesses.

In the rainy season, the floods in Iztapalapa are continuous. All that water is lost through the drain at the helpless look of those who suffer from water shortages; In this delegation alone, about half a million people. Its access depends exclusively on the occasional distribution of tank trucks or the weekly time at which the key is opened and, according to Guadalupe, "a yellow water that smells horrible comes out of the tap . " While the technicians of Isla Urbana install the system in the backyard of their house, this Mexican smiles and says: "Now yes, I am looking forward to rain." The system is very simple: all the rainwater accumulated on the roof (which the owners must keep clean), is distributed through pipes to a filter that removes their impurities and sends it to a large container where it is stored. The program is completely free and the beneficiaries should only register and attend a training talk.

One of the first to sign up for this program was Carmen López, who opens the doors of her home to EL MUNDO to proudly show her particular "cloud juice" crop, as she affectionately calls the rainwater. His life has changed dramatically since Isla Urbana knocked on his door: "Before we only received water once a week and at dawn, we had to always be ready to fill all possible buckets, or for the bathroom we had!" . Now with two or three rains it manages to fill a tank with a capacity of 2,500 liters, enough for two weeks of consumption. Carmen has nothing but words of thanks to the current head of the capital's government, Claudia Sheinbaum, since she says: "A government had never done what she is doing; good things for the people who need it most . "

Until Isla Urbana crossed their path, Felisa and Eugenio had difficulties to cover their basic needs; the water did not reach them. Now they even consider expanding the capacity of their particular rain harvest: "We have so much roofing that, when we have money to condition the patio, we are likely to ask for one more system," says this pair of harvesters. A few meters away, Enrique Lomnitz listens proudly and confesses that he never thought that the doctoral thesis he prepared, along with his partner Renata Fenton, would end up changing the lives of so many people: "The current government has been key to the reality of the project. And although 100,000 may seem like few systems for such a large city, each one counts and helps us get closer to the water balance. " While experts continue to predict the definitive depletion of water in the Mexican capital, in the most humble areas of the city, those who previously suffered shortages become privileged . Only they have stopped relying on running water; now they recycle the vital liquid that nature sends them and so many others waste it.

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