Abstract
Intermittent water supplies (IWS) deliver piped water to one billion people; this water is often microbially contaminated. Contaminants that accumulate while IWS are depressurized are flushed into customers’ homes when these systems become pressurized. In addition, during the steady-state phase of IWS, contaminants from higher-pressure sources (e.g., sewers) may continue to intrude where pipe pressure is low. To guide the operation and improvement of IWS, this paper proposes an analytic model relating supply pressure, supply duration, leakage, and the volume of intruded, potentially-contaminated, fluids present during flushing and steady-state. The proposed model suggests that increasing the supply duration may improve water quality during the flushing phase, but decrease the subsequent steady-state water quality. As such, regulators and academics should take more care in reporting if water quality samples are taken during flushing or steady-state operational conditions. Pipe leakage increases with increased supply pressure and/or duration. We propose using an equivalent orifice area (EOA) to quantify pipe quality. This provides a more stable metric for regulators and utilities tracking pipe repairs. Finally, we show that the volume of intruded fluid decreases in proportion to reductions in EOA. The proposed relationships are applied to self-reported performance indicators for IWS serving 108 million people described in the IBNET database and in the Benchmarking and Data Book of Water Utilities in India. This application shows that current high-pressure, continuous water supply targets will require extensive EOA reductions. For example, in order to achieve national targets, utilities in India will need to reduce their EOA by a median of at least 90%.
Highlights
One billion people receive water from piped networks that are not always pressurized [1, 2], such networks are referred to as intermittent water supplies (IWS) and can be contrasted with Continuous Water Supplies (CWS; 24x7 systems) that are standard in most higherincome countries
Customers that currently consume substantial volumes of flushing water will have a reduced risk of contaminant exposure. Distinguishing between these effects has not been discussed in the literature and may help understand the health impacts of CWS: Ecrumen et al [35] found that CWS only had significant health benefits for lower-income families, which they hypothesized might be due to more frequent usage of water filters in higher-income families. Our model suggests another plausible mechanism: if lower-income families were exposed to flushing water more than higherincome families, the water quality improvements due to CWS would be concentrated in lower-income families
The model suggests that utilities, regulators, and academics alike should take care in distinguishing between water quality during steady-state and flushing phases, and in specifying performance metrics that do not conflict with one another
Summary
One billion people receive water from piped networks that are not always pressurized [1, 2], such networks are referred to as intermittent water supplies (IWS) and can be contrasted with Continuous Water Supplies (CWS; 24x7 systems) that are standard in most higherincome countries. Previous investigations of operational strategies to improve the water quality of IWS have focused on improving the residual chlorine concentration during the steady-state phase [11,12,13] and identifying likely locations of contaminant intrusion during the non-supply period [10, 14]. We apply the model to determine the required extent of leak repair as supply duration and/or pressure is improved under water-scarce scenarios We extend these scaling equations to study how supply duration, supply pressure, and leak repair can affect the volume of intruded, potentially-contaminated fluids present during the flushing and steady-state phases. We quantify the implications of these scaling equations by applying them to self-reported performance indicators for IWS serving 108 million people
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call