Microbiological quality of water vending machines

Abstract

Consumption of water from vending machines has recently increased in the United States. However, studies describing the bacteriological quality of water from these machines are scarce. In this study, bacteriological analyses were performed on samples from 30 water vending machines (WVMs), three of which were sampled weekly for 3 weeks. Bacteriological analyses were also conducted on the nozzle dispensers and the drains of 15 WVMs. Heterotrophic bacteria, total and fecal coliforms, and Pseudomonas aeruginosa were enumerated. Physico-chemical parameters such as pH, temperature, turbidity and residual chlorine were also examined. P. aeruginosa was found in 23% of the water samples and coliform bacteria in 20%. Heterotrophic plate count (HPC) bacteria were found in all samples and 73% had numbers greater than 500 colony forming units (CFU) ml-1. The HPC bacteria ranged from 9 to 48 000 CFU per sampled area on the dispensing nozzle. Total coliforms and Escherichia coli were detected in the drain samples with HPC bacterial concentrations from 1000 to 56 000 CFU per sampled area. No significant correlations were found between the physico-chemical and bacteriological parameters.