Household water quality in areas irrigated with wastewater in the Mezquital Valley, Mexico.

Wastewater for irrigation in low- and middle-income countries can recharge aquifers and potentially contaminate supply sources. The infiltration rate has increased 13-fold in Mexico's Mezquital Valley, the largest agricultural area wastewater-irrigated worldwide, thus we assume that wastewater had contaminated supply sources. Fecal indicator bacteria (FIB) counts were enumerated in household water of two wastewater-irrigated areas, Tula and Tlahuelilpan, and a groundwater irrigated area, Tecozautla. During 2016-2017, household water, wastewater, and groundwater were sampled, analyzing fecal coliforms, fecal enterococci, and Escherichia coli, following membrane filtration procedures, and confirming the presence of E. coli by polymerase chain reaction. Nearly 50% of household water contained fecal contamination of up to 4.62 × 104 CFU/100 mL. Significant differences between FIB counts in household water from Tula and Tecozautla were observed by Kruskal-Wallis and Dunnett tests. Household water samples from Tula contained highest FIB counts. Wastewater from Tula and Tlahuelilpan contained counts of six orders-of-magnitude of FIB. Counts were high when residual chlorine was <0.2 mg L-1 and underwater storage. This research serves as a baseline to observe improvement with a newly installed wastewater treatment plant. Safe irrigation wastewater reuse should be performed under strict surveillance, considering human safety a priority.

Microbial Indicators, Opportunistic Bacteria, and Pathogenic Protozoa for Monitoring Urban Wastewater Reused for Irrigation in the Proximity of a Megacity.

In Latin America and the Caribbean, with a population of approximately 580 million inhabitants, less than 20 % of wastewater is treated. Megacities in this region face common challenges and problems related with water quality and sanitation, which require urgent actions, such as changes in the sustainable use of water resources. The Mexico City Metropolitan Area is one of the most populous urban agglomerations in the world, with over 20 million inhabitants, and is no exception to the challenges of sustainable water management. For more than 100 years, wastewater from Mexico City has been transported north to the Mezquital Valley, which is ranked as the largest wastewater-irrigated area in the world. In this study, bacteria and pathogenic protozoa were analyzed to determine the association between the presence of such microorganisms and water types (WTs) across sampling sites and seasons in Mexico City and the Mezquital Valley. Our results show a difference in microbiological water quality between sampling sites and WTs. There is no significant interaction between sampling sites and seasons in terms of bacterial concentration, demonstrating that water quality remains constant at each site regardless of whether it is the dry or the rainy season. The results illustrate the quantity of these microorganisms in wastewater, provide a current diagnosis of water quality across the area which could affect the health of residents in both Mexico City and the Mezquital Valley, and demonstrate the need to transition in the short term to treat wastewater from a local to a regional scale.