Controlling water quality in intermittent supply systems

Abstract

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.

Intermittent Domestic Water Supply: A Critical Review and Analysis of Causal-Consequential Pathways

“…Nevertheless, private storage causes poor water quality [46,55,110], pressure surges in the system [13,48], and consumer overdraw [2,23,35,50,76,114]. Additionally, some authors found that private storage wastes water [23,35,70,81,128], while others found that in systems with more reliable supply, water storage did not result in more water use [18,47]. This difference relates to the extent to which consumers need to account for risk aversion and supply security in their water supply [50], and will be discussed further below.…”

“…For example, one researcher describes intermittent water arriving during a 24 h period is an unreliable supply [116], although for [34], water arriving for less than 24 h a day (but within a given 24 h period) is intermittent. Others define intermittency as water arriving at intervals of hours, days, or weeks [21,35]. While some studies are very clear about the service conditions [115], many studies do not provide enough information to characterize water delivery service.…”

Household characteristics associated with home water treatment: an analysis of the Egyptian Demographic and Health Survey

“…Approximately one third of DHS respondents reported interruptions to their water supplies. Such interruptions are known to compromise water quality (Coelho et al 2003), for example as low or negative water pressure draws in contaminated water into piped networks. The DHS also suggests that the prevalence of child diarrhoea in Egypt is comparable with those derived from recent DHS in sub-Saharan Africa with lower improved water source coverage.…”

Evaluation of the Water Scarcity Energy Cost for Users

“…The network is subjected to cyclical filling phases and emptying periods during which the distribution system is unpressurised and it may occur that pollutants enter the pipes. In this period of stagnation microbial re-growth can be promoted, further compromising water quality [8]. Furthermore, these pollutants are carried through the network to the point-of-use when the pipes become completely full and the distribution system is in steady state conditions.…”

“…Private tanks modify the demand profile of typical domestic users: they are usually filled in a very short period after the reactivation of water service, leading to very high peaks in flow, and, then, in velocity in the pipe network [6,7]. These peaks, and the peaks in pressure due to the network filling process, lead to biofilm detachment and microbial cells release events that increase risk for the final user [8,12]. Moreover, private tanks are often over-designed because the intervals between supply periods are variable (ranging from a few hours to several days).…”