In 2011, a severe flood occurred in Thailand, covering nearly half the country in water for several months. The
contamination of floodwater and subsequent contamination of water for human consumption could have potentially
led to a widespread health crisis. However, to date, no study has been conducted to determine the safety of
the waters used for human consumption in Thailand during the severe flood. Therefore, we conducted microbiological
analysis of 4 kinds of water (floodwater, river water, tap water, and filtered tap water) collected from
industrial and residential areas that were damaged due to flooding. Higher net levels of bacteria were found in
water with a higher turbidity. No clear trend was observed in the pH value of all 4 water samples. The level of
total bacterial contamination in the water sampleswas estimated by real-time quantitative polymerase chain reaction
(PCR). Eleven of the 12 tap water samples and all of the filtered tapwater samples had a total bacterial load
that exceeded the Thai water quality standards. One of the tap water samples and one of the filtered tap water
samples were found to be positive for Shigella sp., although none of the floodwater samples showed detectable
levels of this pathogen as determined by PCR analysis. One of the samples of floodwater was also found to be positive
for Leptospira sp., but none of the tap water or filtered tap water samples were positive. Most of the tap
water samples and all filtered tap water samples were found to be contaminated with Vibrio cholerae. Bacterial
contamination in water samples was also analyzed by denaturing gradient gel electrophoresis (DGGE) analysis.
These results revealed that several microorganisms were transferred via floodwater to different areas in the central
part of Thailand and cross-contaminated between floodwater and water for human consumption