Quality assessment of an aquifer recharged with wastewater for its potential use as drinking source: "El Mezquital Valley" case.

Mexico City, with a population of 18 million, has been sending its wastewater for more than 100 years to the Tula Valley where it is used to irrigate 90,000 ha. Due to the large wastewater volume (60 m3/s) sent through unlined channels, combined with the use of very high irrigation rates, artificial recharge of the local aquifer has been occurring. This recharge is estimated in more than 25 m3/s. As a consequence, the water table has raised and several springs have appeared in the last decades with flows between 100 to 600 L/s. These springs and several wells are the water sources in the region. An evaluation of the Tula Valley aquifer quality was performed to analyze the use of such water as source of drinking water for Mexico City. The work is divided into 5 individual projects: (a) drinking water quality in the Tula Valley; (b) water availability in the Tula Valley; (c) wastewater treatment due to its use for irrigation, (d) use of membrane processes to treat groundwater; and (d) biota developed in the new surface water reservoirs. Results show that it is feasible to use this reclaimed water as drinking source.