In countries suffering from chronic water shortages, water distribution systems are often operated on an intermittent basis, leaving them unpressurised and allowing ingress of contaminated groundwater, particularly in areas lacking sewerage systems. The periods of stagnation can promote microbial regrowth, further compromising water quality. On the other hand, peaks in pressure and velocity in the pipe network lead to biofilm detachment events, thus releasing microbial cells that may escape the regular quality monitoring procedures and thus increase risk for the consumer. Finally, intermittent supply requires consumers to store water in household storage tanks, which often encourage bacterial regrowth. This paper reports on research undertaken in Jordan, Lebanon, Palestine, the UK and Portugal, which provided an improved understanding of the factors controlling bacterial concentrations in intermittent supplies, and presents an overview of the most important aspects of water quality control in intermittently operated networks.

In parts of the world with severe water shortages, distribution mains may only supply water for a few hours each week, and householders must store the water in tanks on the rooftop or in a reservoir beneath the house. When these intermittent supplies are stored over a period of several days, water quality may rapidly deteriorate, creating a health risk to the consumer. A study conducted in Amman, Jordan, examined the extent and characteristics of microbial regrowth in different types of household storage tanks as well as the parameters influencing this regrowth. Study results showed that heterotrophic bacterial counts increased significantly from log 1.7 to log 5.2 and log 5.7 cfu/mL after water was stored for four and seven days. Microbial regrowth was dominated by Actinomycetes, Pseudomonas species, and Moraxella spp. The different materials of the household tanks (polyethylene, fiberglass, and cast iron) did not significantly influence the total bacterial count of the stored water. Temperature was the factor that most influenced microbial regrowth in household tanks. More research on this topic is needed, particularly to identify the most effective means of reducing the scale of regrowth. To reduce the public health hazard associated with drinking stored water (especially in hot climates), the authors propose various strategies including point‐of‐use devices, secondary chlorination in household tanks, and annual tank cleaning.

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