Measured and Modeled Comparisons of Chemical and Microbial Contaminants in Tap and Bottled Water in a US-Mexico Border Community

Tap water quality concerns and advertisements often drive increased bottled water consumption, especially in communities with historical tap water quality problems (e.g., Nogales, Arizona). The study objective was to assess the contamination of municipal tap and bottled water in Nogales, Arizona. Bottled (sealed, open/partially consumed bottles, and reusable containers for vended water) and tap water samples were collected from 30 homes and analyzed for chemical and microbial contaminants. Fisher exact tests and Wilcoxon rank sum tests were used to compare the proportions of positive samples and contaminant concentrations between tap and bottled water samples. While none of the chemical contaminants were above MCLs, there were statistically significantly greater concentrations and proportions of positive samples for some contaminants, including arsenic, in tap versus bottled water. Escherichia coli concentrations were >0 CFU/100 mL in some unsealed bottled water samples but not in sealed bottles. This study demonstrates that (1) the measured concentrations in tap and bottled water likely pose low risks as they are below the MCLs, (2) more education in this community on hygiene maintenance of refillable or opened bottled water containers is needed, and (3) using tap water over bottled water is advantageous due to likely lower E. coli risk and lower cost.