Factors Contributing to Chlorine Decay and Microbial Presence in Drinking Water Following Stagnation in Premise Plumbing

Premise plumbing is the part of the drinking water distribution system closest to the point of use. Since premise plumbing is characterized by a long residence time, elevated temperature, and reduced levels of disinfectant residue, drinking water in premise plumbing typically experiences elevated levels of microbial presence as compared to finished water exiting water treatment utilities, particularly under stagnation conditions frequently encountered in premise plumbing. Thus, stagnant drinking water in premise plumbing may represent an important source of public health risk. Therefore, the objective of this study is to identify factors contributing to the deterioration of microbiological quality of stagnant drinking water in premise plumbing. Results from this study indicated that the service age of premise plumbing system is positively correlated to the concentration of microorganisms in stagnant drinking water; Another factor contributing to microbial contamination is the usage pattern, with systems experiencing lower levels of water consumption exhibiting greater microbial contamination than those having greater water usage patterns; Since disinfectant residue is an important determinant of microbial contamination, the loss of free chlorine as the most common disinfectant residue was further examined. My results demonstrate that pipe material has significant impact on the decay rate of free chlorine, with copper pipe showing the greatest chlorine decay rate, and PVC pipe showing the slowest. The deposits onto the pipe wall appear to reduce the rate of chlorine decay, likely forming a barrier between the pipe material and water, which slows down the reaction between the pipe wall and the disinfectant. Moreover, pipe diameter and temperature could significantly influence the rate of chlorine decay, with greater diameter leading to smaller surface-to-volume ratio and subsequently a slower chlorine decay rate. As expected, elevated temperature was shown to accelerate chlorine loss. These results provide important insights into the mechanisms of chlorine decay in premise plumbing and the factors contributing to the deterioration of the microbiological quality of drinking water in premise plumbing, which could facilitate the development of effective strategies for controlling water quality in premise plumbing and reducing public health risks from waterborne infectious diseases.