For over 100 years farmers in Hidalgo State use “the black waters” (wastewater) from Mexico City to irrigate their land.
So when word got out that the government was finally going to build a giant wastewater treatment plant, one might have expected the farmers around here to be excited. Instead, they were suspicious.
“Without that water, there is no life, “ said Gregorio Cruz Alamilla, 60, who has worked his family’s 12-acre farm since he was a boy.
Mr. Cruz knows the water is loaded with toxic substances, including chemicals dumped by factories, and he tires of clearing his field of plastic bottles and wrappings every time he irrigates.
But like many others here, he worries that treating the water, though it may remove harmful contaminants, will also strip away some of the natural fertilizers that even the authorities here say have helped make this valley so productive. And despite the government’s assurances, the farmers here suspect the worst: that once the water is treated, it will be pumped back to Mexico City, leaving the farms dry.
Wastewater reuse for irrigation is common throughout the developing world, but nowhere on the scale of Mezquital Valley with its 350 square miles (906 square kilometres) of irrigated fields.
But now, Mexico City (pop. 20 million) is building a stormwater drainage system and treatment plant to deal with the growing problem of flooding during the rainy season.
“It was a predictable problem, but we never paid enough attention to it,” said Ernesto E. Espino de la O, who manages the treatment and water supply project for the National Water Commission. A collapse of the crumbling system, warned one study from Mexico’s National Autonomous University of Mexico, would be catastrophic, flooding large parts of the city.
Engineers have started to construct a 38.5-mile (62 km) drainage tunnel that will transport stormwater to the town of Atotonilco, where a wastewater treatment is plant is planned.
The plant, which is budgeted to cost $1 billion and will begin operating in 2012, will clean 60 percent of the city’s wastewater. The water commission’s measurements show that the water is laced with heavy metals like lead and arsenic, filled with high levels of pathogens and parasites, and weighed down by grease.
But the farmers “are worried that the treatment plant will take out the nutrients, that the water will go back to Mexico City and that it will be privatized,” said Filemón Rodríguez Castillo, the director of the main irrigation district here. “The water is very much appreciated here, independent of the fact that it smells so ugly, that it stinks.”
One of his jobs is to persuade local residents that even though the residents of Mexico City will have to pay to have their water treated, they will not get it back.
The main benefit of irrigating with clean water, he has told them, is that they will be able to grow many kinds of vegetables, which are now restricted to protect consumers from illness.
Officials here now direct farmers not to grow crops in which the edible part comes into contact with the irrigation water and is eaten raw, ruling out vegetables like lettuce, carrots or beets. Alfalfa is permitted because it is used as animal feed. But enforcement is spotty and the farmers abide by an elastic interpretation of the regulations, planting broccoli and cauliflower, for example.
To the farmers here, whose sturdy opinions match their surprisingly good health, the proof that their water is good is in what they see around them. “Plants won’t absorb poison; they would die,” said Jesús Aldana Ángeles, a 75-year-old fifth-generation farmer, who was watching his small flock of sheep munch on the remains of his harvested alfalfa field. “There is no better laboratory than the ground. The earth absorbs everything. It purifies it, it treats it.”
Read more about wastewater irrigation read “Wastewater irrigation and health : assessing and mitigating risk in low-income countries”.
Related web site: WHO – Safe use of wastewater, excreta and greywater
Source: Elisabeth Malkin, New York Times, 04 May 2010