Water utilities worldwide lose 128 billion cubic meters annually, causing annual monetary losses estimated at USD 40 billion. Most of these losses occur in developing countries (74%). This calls for a rethinking of the challenges facing water utilities in developing countries, foremost of which is the assessment of water losses in intermittent supply networks. Water loss assessment methods were originally developed in continuous supply systems, and their application in intermittently operated networks (in developing countries) is hindered by the widespread use of household water tanks and the unauthorised consumption. This study provides an extensive review of existing and new methods and (software) tools for water loss assessment. As the volume of water loss varies monthly and annually according to the amount of water supplied, this study proposes procedures to normalise the volume of water loss in order to enable water utilities to monitor and benchmark their performance in water loss management. In addition, a practical method was proposed for estimating apparent losses using data of WWTP inflows, enabling future real-time monitoring of losses in networks. The study then examines the applicability of minimum night flow analysis in the case of intermittent supply, and models the accuracy of the customer water meter under intermittent supply conditions. Finally, the study provides guidance to improve the accuracy of water loss assessment in intermittent supply networks. Accurate assessment of water loss is a prerequisite for reliable leakage modelling and minimisation, as well as planning for, and monitoring of water loss management in distribution networks.@en

Intermittent supply is common worldwide. It triggers households with piped connection to adjust the supply scheme by the use of a water tank with a float valve (FV) at the entrance, which has a major influence on the water meter accuracy. This study investigated the impact of the water tank with a FV on the performance of water meters under intermittent and continuous supply conditions, using laboratory experiments, field measurements, and hydraulic modeling. Results revealed that the inflow rates into the water tank are consistently lower than the outflow rates of the tank. This will always be the case owing to the balancing mechanism of the tank. The flows that pass through the water meter represent the inflows into the tank. Therefore, higher metering errors and more apparent losses are expected for a combination of a water tank, FV, and continuous supply. Besides, different FV types have different hydraulic characteristics. Larger FVs with higher discharge rates tend to maintain the water level close to the full level in the tank and conferred longer periods of low flows, worse meter performance, and more apparent losses. For intermittent supply, results confirmed that higher intermittency levels lead to improved performance of water meters and reduce the apparent losses. This points to the complication in transformation from intermittent to continuous supply worldwide. In this case, water utilities should expect higher meter errors and more revenue losses unless the meter replacement policy recognises lower flows passing through the meter.

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Reducing all water loss components to zero is neither technically possible nor economically viable. The water loss components should be accurately assessed and prioritised for a reduction. This paper investigates all methods that break down the water losses in distribution networks into apparent and real losses. Their accuracies and uncertainties are discussed and applications to three case studies in developing countries are presented. The results show that different methods estimate the water loss components differently. Consequently, different reduction measures are planned and prioritised. Interestingly, the least accurate methods have a low level of uncertainty, but more realistic assumptions yield higher uncertainties. This suggests that the uncertainty analysis only assists in improving the outputs of each of the methods but does not demonstrate their accuracy. The cost of water loss varies depending on the used assessment method and the economic feasibility of the reduction measures is significantly influenced. The water loss components should therefore be assessed for the whole network using at least two methods to reasonably model and monitor the loss reduction in water distribution networks.

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Water utilities should monitor their nonrevenue water (NRW) levels properly to manage water losses and sustain water services. However, monitoring NRW is problematic in an intermittent water supply regime. This is because more supplied water to users imposes higher volumes of NRW, and supplying significantly less water results in an unmet water demand but interestingly less NRW. This study investigates the influence of the amount of water supplied to a distribution system on the reported level of NRW. The volume and indicators of NRW all vary with variations in the system input volume (SIV). This is even more critical for monitoring NRWfor systems shifting from intermittent to continuous supply. To enable meaningful monitoring, the NRW volume should be normalised. Addressing that, this research proposes two normalisation approaches: regression analysis and average supply time adjustment. Analysis of the NRW performance indicators showed that regression analysis enables the monitoring of NRW and tracking its progression in an individual system only, but not for a comparison with other systems. For comparing (or benchmarking) a water system to other systems with different supply patterns, the average supply time adjustment should be used. However, this approach presents significant uncertainties when the average supply time is less than eight hours per day.@en

A significant portion of the water supplied to people doesn't reach its valid users but instead leaks out of the distribution network, causing water wastage, revenue loss and contamination risks. This paper analyses the leakage rate, leakage components and leakage reduction potential. A minimum night flow (MNF) analysis was carried out on a district metered area (DMA) in an intermittent supply system in Zarqa, Jordan. Leakage was modelled and leakage reduction policies were analysed. Results show that MNF occurs at night or during day time depending on the water levels in customer tanks, implying that one-day MNF analysis cannot be carried out in intermittent supplies and the estimation of the legitimate consumption during MNF is more influential. The potential water savings of the different leakage reduction measures (pressure management; leakage detection; response time minimization) are separately analysed in the existing models in the literature, leading to significant overestimation of the total leakage reduction potential, while these measures are influencing each other. Pressure reduction lowers the failure frequencies but limits the potential of leakage detection surveys, as leaks will become harder to hear and detect. Investigating the inter-dependency relations of these measures is therefore essential for reasonable leakage reduction modelling and planning.

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