Bacterial survival and regrowth in drinking water systems.

Weekly variations in free and total chlorine residuals, and their impact on microbial concentrations were monitored for the IIT Kharagpur (IITKgp) water supply to determine possible correlations between heterotrophic bacterial density, total and faecal coliform density, and total and free chlorine residuals. All correlations between HPC, coliforms and free and total chlorine residuals were found to be insignificant, suggesting that coliform survival and growth are not inhibited by low levels of residual chlorine ranging from 0.01 to 0.41 mg Cl2/L and total chlorine ranging from 0.02 to 1.23 mg Cl2/L. Growth studies were carried out to measure bacterial growth rates in chlorinated drinking water using turbidity. An effort was also made to establish correlations between Cell Density (cfu/L) and Turbidity (NTU), which would allow turbidity to be used as a tool for measurement of bacterial growth in real time. Bacteria were grown in nutrient broth solutions diluted 10-fold with chlorinated tap water to simulate low substrate chlorinated drinking water environments and the average growth rate was 0.196 +/- 0.049 1/h (n = 5, CoV = 25%). No bacterial inocula were added to these samples and chlorine residuals in these samples were 0.14 +/- 0.06 mg Cl2/L and 0.06 +/- 0.05 mg Cl2/L for total chlorine and free chlorine, respectively.

Chlorinated drinking water, cancers and adverse health outcomes in Gangtok, Sikkim, India.

Long-term impacts of drinking chlorinated water on the incidence of cancers and other adverse health outcomes were assessed in a population-based cross-sectional study. The study was conducted by comparing a group exposed to chlorinated drinking water for more than thirty years with control groups with less or no exposure to chlorine. A house-to-house survey was completed to gather information on residential history, age, education, income, source and extent of treatment of water and health characteristics. All residents below thirty years of age were excluded from the database used for analyses to ensure that the groups were comparable. Fourteen cancer cases were found in the long-term exposed groups of 1085 persons and 9 cancer cases in the two control populations of 725 persons. The odds ratio for cancers (OR) was 1.05 (95% CI = 0.43-2.65) and is not statistically significant. Odds ratios for gastrointestinal disorders, kidney problems and skin infections were statistically significant ranging from 2.06 (95% CI = 1.01-4.17) to 2.2 (95% CI = 1.45-3.33). These OR values indicate that there is no significant association between the incidence of cancer and exposure to chlorinated water while chlorinating drinking water significantly reduced the incidence of non-carcinogenic adverse health effects like gastrointestinal diseases, skin infections, and kidney diseases.