Longitudinal Study of Microbial Diversity and Seasonality in the Mexico City Metropolitan Area Water Supply System

Abstract

In the Mexico City metropolitan area (MCMA), 70% of the water for 18 million inhabitants is derived from the Basin of Mexico regional aquifer. To provide an overview of the quality of the groundwater, a longitudinal study was conducted, in which 30 sites were randomly selected from 1,575 registered extraction wells. Samples were taken before and after chlorine disinfection during both the rainy and dry seasons (2000-2001). Microbiological parameters (total coliforms, fecal coliforms, streptococci, and Vibrio spp.), the presence of Helicobacter pylori, and physicochemical parameters, including the amount of trihalomethanes (THMs), were determined. Although microorganisms and inorganic and organic compounds were evident, they did not exceed current permissible limits. Chlorine levels were low, and the bacterial counts were not affected by chlorine disinfection. Eighty-four bacterial species from nine genera normally associated with fecal contamination were identified in water samples. H. pylori was detected in at least 10% of the studied samples. About 40% of the samples surpassed the THM concentration allowed by Mexican and U.S. regulations, with levels of chloroform being high. The quality of the water distributed to the MCMA varied between the rainy and dry seasons, with higher levels of pH, nitrates, chloroform, bromodichloromethane, total organic carbon, and fecal streptococci during the dry season. This study showed that the groundwater distribution system is susceptible to contamination and that there is a need for a strict, year-round disinfection strategy to ensure adequate drinking-water quality. This situation in one of the world's megacities may reflect what is happening in large urban centers in developing countries which rely on a groundwater supply.

Microbial ecology of drinking water distribution systems

“…Uncontrollable events, such as seasonal fluctuations of precipitation, can lead to even greater complexity. For example, a study of Mexico City's chlorinated DS found that levels of fecal streptococci were significantly higher in the dry season than in the wet season, whereas H. pylori levels remained fairly constant through the seasons [54]. This illustrates that uncontrollable complexity such as seasonal precipitation can lead to species-specific responses.…”

Household’s Perception of Water Quality and Willingness to Pay for Clean Water in Mexico City

“…Furthermore, these are studies that support the public's perception about the management and maintenance of the water distribution system, indicating that it is inadequate and insufficient, with 40% water loss due to leaks (Morales-Novelo and Rodríguez-Tapia 2007;Perló and González 2005) or significant fluctuations of the water quality (Mazari-Hiriart et al 2005). It should be noted that the research does not focus on poor management of the provider and is mainly based on the public's perception about water quality and supply, not taking into account the consumer's failure to properly maintain in-home water deposits such as pipes, faucets, roof tanks and underground cisterns.…”

Potentially pathogenic nontuberculous mycobacteria found in aquatic systems. Analysis from a reclaimed water and water distribution system in Mexico City

“…70% of the water demand for a densely populated area with ca. 20 million inhabitants [15]. The third aquatic system was composed of a complex canal network (189 km) located in Xochimilco, south of the MCMA.…”