Almost 200,000 acres of land in the fertile Mezquital Valley are irrigated with the untreated sewage of Mexico City. Every drop of rain, urban runoff, industrial effluent, and sewage in Mexico City is sent to the Mezquital Valley through a 60 kilometer pipe. Soils in this valley have been continuously irrigated with urban wastewater since 1901, longer than any other soil in the world. The capacity of these soils to produce conditions in which agriculture can be practiced safely and produce healthy crops depends on a complex negotiation between soil chemistry, farming practices, public policy, land management, and the urban design of Mexico City. Without this wastewater, the Mezquital Valley would be a desert, as it falls into the UN’s “drylands” climate category, where rates of evapotranspiration exceed precipitation.
Currently, more than 40% of the Earth’s surface is classified as “drylands.” In the context of a warming planet, the world simply cannot afford for urban wastewater reuse to fail. Water is scarce, and food security is fragile. In this context, the question becomes: what would the city look like if it needed to produce a fertile agricultural soil from its waste? What would the farm look like if it better anticipated its material connection to the bodies of 20 million people and the effluent of urban life?
Seth Denizen is a researcher and design practitioner trained in landscape architecture and human geography.