Comparative analysis of total bacterial count in drinking water before and after disinfection in rural areas of five provinces in China

Objective To compare the total bacterial count in drinking water before and after disinfection in rural areas, and to evaluate the quality and effect of drinking water disinfection.

Methods Based on the use of disinfection and the presence of microbial contamination, 14 each of water plants with and without disinfection were randomly selected in 7 counties of 5 provinces in China. The total bacterial count of source, finished, and tap water samples from water plants with nondisinfection, as well as the disinfectant residual in finished and tap water samples from water plants with disinfection, were determined every other 12 days (a total of 15 determinations of each kind of water plants per year). The differences in median bacterial count, detection count and over standard rates among source, finished, and tap water samples were compared by the median test, Krushal-Wallis test, and χ² test, respectively.

Results The M (P₂₅, P₇₅) of 1 182 source, finished, and tap water samples were 100 (26, 147), 33 (5, 130) and 55 (5, 140) CFU/mL, respectively. The medians of total bacterial count were significantly different (χ² = 43.65, P < 0.001). When residual disinfectant in finished and tap water samples complied with the standard, the M (P₂₅, P₇₅) of source, finished, and tap water samples were 91 (47, 142), 7 (2, 23) and 10 (3, 38)CFU/mL, respectively. The median of total bacterial count was significantly different between finished and source water samples (χ² = 89.50, P < 0.001) and between tap and source water samples (χ² = 71.3, P < 0.001). The over standard rates of total bacterial count of source, finished, and tap water samples were 44.4%, 2.3% and 6.0%, respectively. The over standard rates were significantly different between finished and source water samples (χ² = 65.95, P < 0.001) and between tap and source water samples (χ² = 51.89, P < 0.001). The total bacterial count decreased by 91% in finished water and by 88% in tap water compared with source water. The total bacterial count increased by 50% in tap water compared with finished water. The changes in total bacterial count were significantly different among the three types of water (χ² = 129.74, P < 0.001). When water was not disinfected or residual disinfectant did not comply with the standard, the median total bacterial count and over standard rates were not significantly different among source, finished, and tap water samples (P>0.05). The change in total bacterial count was not significantly different between finished and source water samples, tap and source water samples, and tap and finished water samples (P>0.05).

Conclusion Disinfection can effectively reduce the number of microorganisms in drinking water. Drinking water disinfection is one of the effective measures to improve the safety of water supply for rural residents.