Assessment of Microbiological Water Quality after Low Pressure Events in a Distribution System

Abstract

Previous studies have monitored pressure transients and fluctuations in several distribution systems and low pressures (<20 psi) were commonly recorded, including a few negative pressure events. During a low-pressure event, microbiological contamination of the distribution system can result due to intrusion of contaminated water. However, no study to date has attempted to assess microbiological water quality in temporally-composited samples collected immediately following a pressure drop, nor have temporally-composited samples been collected to statistically characterize microbiological water quality in a distribution system or point of entry. The findings presented here represent preliminary results from an ongoing study monitoring a large distribution system for pressure fluctuations and assessing microbiological water quality in 100-L water samples collected immediately after the occurrence of low pressure events. Pressure monitoring by up to six pressure loggers located at the point-of-entry (POE) and throughout the distribution system for four months found 11 distinct low pressure events. Of these, three separate events resulted in minimum pressure readings in the distribution system of 0 psi. The data indicate that these events can be both isolated and system-wide, and that system-wide events were associated with pressure drops at the POE. In addition to providing additional data on the occurrence of low pressure events in the distribution system, these data will assist in determining appropriate locations of automated monitoring and sampling units designed to collect water samples following low pressure events. This paper was presented at the 8th Annual Water Distribution Systems Analysis Symposium which was held with the generous support of Awwa Research Foundation (AwwaRF).