Impact of pathogen intrusion in water distribution network under sustained low pressure conditions

Abstract

Drinking water distribution networks across the world are of high average age, and in many cases in poor condition due to delayed or inadequate maintenance. These conditions in combination with regular water distribution network pressure losses present significant challenges for water utilities in providing safe water. This study presents an assessment of human health risk resulting from pathogen intrusion in a water distribution network (WDN) under sustained low pressure events. Two low pressure causing events, a pump failure, and extreme water use through a fire hydrant, were simulated. EPANET water quality/hydraulic model was used for simulating transport and fate of pathogen intrusion in a WDN under sustained low pressure conditions. Quantitative microbial risk assessment (QMRA) was used for determining the infection risks for the people exposed. The areas with sustained low negative pressure were identified as vulnerable zones where the distribution of pathogens was investigated using EPANET and risk determined with QMRA. The results indicate that 2.3% of the network was at risk of pathogen intrusion in the event of a pump failure while 2.9% of the network could be at risk from emergency fire events. The QMRA result indicates a 100% probability of infection of the population exposed during the short event time. The factors that influence pathogen intrusion and hence the risk were found to be the duration and magnitude of the low pressure event, affected section length, and size of leakage. Overall, the infection risks exceeded the “United States Environmental Protection Agency's” recommended limit of 10-6 persons infected per day hence mitigation measures were necessary to minimize the risks in case of these events. Measures that reduce the exposure to consumers, such as pressure and water quality management, leak repair, and isolation of affected areas, were considered primary measures for reducing risks. Sensors were thus proposed to act as early warning systems in the event of pressure or quality change.