Assessing the public health risk of microbial intrusion events in distribution systems: conceptual model, available data, and challenges

Low and negative pressure events in drinking water distribution systems have the potential to result in intrusion of pathogenic microorganisms if an external source of contamination is present (e.g., nearby leaking sewer main) and there is a pathway for contaminant entry (e.g., leaks in drinking water main). While the public health risk associated with such events is not well understood, quantitative microbial risk assessment can be used to estimate such risk. A conceptual model is provided and the state of knowledge, current assumptions, and challenges associated with the conceptual model parameters are presented. This review provides a characterization of the causes, magnitudes, durations and frequencies of low/negative pressure events; pathways for pathogen entry; pathogen occurrence in external sources of contamination; volumes of water that may enter through the different pathways; fate and transport of pathogens from the pathways of entry to customer taps; pathogen exposure to populations consuming the drinking water; and risk associated with pathogen exposure.     

Changing from intermittent to continuous water supply and its influence on service level benchmarks: a case study in the demonstration zone of Nagpur,India

A dearth in infrastructure and operations significantly reduces the expected benefits of safe drinking water provision. Intermittent water supplies are characterized by inefficient demand and supply management owing to operational inadequacies eventually causing physical deterioration of infrastructure and inconvenience to consumers, resulting in consumer dissatisfaction. Conversion from intermittent to continuous water supply was undertaken in a demonstration zone of Nagpur, India, with a population of about 150,000 people. Data related to the infrastructural, operational, managerial and financial capabilities were used to determine service level benchmarks (SLBs) — pre- and post-intervention — to quantify the improvement due to continuous water supply interventions. The post-intervention data analysis clearly indicated substantial improvement in post-intervention SLBs, consequently paving the way for the conversion of the water supply of the entire city to continuous mode.