Comparative microbial flora study of tap water and bottled water in the United States using BOD protocol

The Flint, Michigan water crisis in 2016 has raised nationwide concern about tap water quality. In the past two decades, the consumption of bottled water has risen in the United States, becoming a commonplace alternative for tap water and other beverages. Despite this rise in popularity, bottled water, which is regulated by the FDA, is tested less frequently and less strictly than tap water, which is regulated by the EPA. So far, few water quality reports have been issued by independent accredited institutions to compare the microbial flora of tap water to that of bottled water sold in the United States. Therefore, this project was designed to compare the heterotrophic bacterial populations in tap water and bottled water under current regulations. I used cultivation-dependent methods to develop a protocol to compare the microbial loading of tap and different types of bottled water and to determine whether those heterotrophic bacteria were gram-negative or gram-positive. For this purpose, tap water collected at Bard College was compared with domestic brand bottled water purchased at a local grocery store through a biochemical oxygen demand assay (BOD). The BOD of spring water and purified water were also compared. The BOD assay was accompanied by a spread plate assay. Heterotrophic bacterial strains were isolated at two temperatures (20 ± 2 °C and 37 ± 2 °C) on R2A agar. Most representative strains were identified using Gram stain. Tap water was found to have higher BOD5 and CFUs/mL than bottled water. Alkaline spring bottled water has higher BOD5 and CFUs/mL than the other spring water sample and purified water. Correlations between BOD5 and CFUs/ml and correlation between BOD5 and pH value were also analyzed. Consequently, BOD assay was found to be a feasible method to estimate the microbial load in drinking water