Microbiological Quality of Bottled Water Obtained from Mexican Small Water Purification Plants: A Pilot Study, Carried Out in Morelia (Central Mexico)

The aim of this work was to begin to determine the microbiological quality of bottled water samples obtained from small purification plants located in Morelia, Michoacan, Mexico. Various microorganisms were taken into account, including nontuberculous mycobacteria (NTM) species. All 20 samples analyzed were positive for aerobic mesophilic bacteria. Eleven (55%), 6 (30%), and 2 (10%) water samples were positive for total coliforms, fecal coliforms, and Escherichia coli, respectively. In total, 18 (90%) of the water samples exceeded the maximum allowed limit stipulated by Mexico’s official guidelines, establishing that purified water must not exceed the limit of 2 log CFU/mL (100 CFU/mL) of aerobic mesophilic bacteria and the presence of total coliforms must not be detectable in any 100 mL (<1.1 most probable number/100 mL) of sample. Five (25%) of the purified water samples were positive for NTM. The findings clearly showed that most of the purified bottled water samples had unsatisfactory microbiological quality and some harbored NTM associated with human illness. Therefore, the study as a pilot points to a need for Mexican health authorities to perform frequent monitoring of purified water producers to verify compliance with standards regarding microbial safety.