The Autonomous Metropolitan University of Mexico (UAM) has developed biological methods for treating wastewater that are more effective than the standard approaches, which use physical and chemical processes. The biological method, patented by the university, puts the contaminated water through an anaerobic process (without oxygen) and a treatment with microscopic algae, which can later be used as fertilizer. The purification is completed using water lilies.

But there are no policy or financial incentives to use this bio-technique, which despite requiring higher initiation investment, over the long term is cheaper than other water treatment methods.

“The legislation is very lax, and there is not much oversight, so many companies, especially the smaller ones, opt to dump the contaminated water without treating it,” Mónica Meraz, a researcher at UAM's biotechnology department, told Tierramérica.

In Mexico, just one-third of wastewater goes through purification.