The ecology of acid‐fast organisms in water supply, treatment, and distribution systems

Eight locations in each of two water utilities were sampled for 18 months in order to collect data on acid‐fast organisms, total coliforms, standard plate count, membrane standard plate count, free and total chlorine residual, total organic carbon (TOC), pH, turbidity, and temperature. These data were analyzed by using computerized statistical packages. In raw water, densities of acid‐fast organisms correlated with concentrations of total coliforms and the level of turbidity. Sand filtration removed acid‐fast organisms, and the densities of acid‐fast organisms decreased with increasing distance from the treatment plant. Conventional terminal chlorination appeared to have no statistically significant effect on the density of the organisms leaving the plant. Overall, chlorine residuals had a negative effect on densities of acid‐fast organisms, whereas turbidity and TOC had positive effects on microbial concentrations.