Estimation of Water Balance and Water Losses in Water Utilities – Experiences from the Belgrade Waterworks - page 3

 

Methods for Assessing Water Losses

For estimation of water balance components various data and empirical relations can be used, including data on reported leakages, water tank overflows and other data. Measurements of water flows within the system are of essential importance for water balance estimations. It is important to note that estimation of the water balance components are not exact, but contain uncertainties which are consequence of measurement inaccuracies, unreliable data, estimations and other factors (Lambert, 2003). Therefore, detailed field measurements are needed to increase accuracy and reliability of water loss components.

Best practices in this field suggests that water supply distribution networks should be divided in District Metering Areas (DMA). DMA is a defined area of the distribution system that can be isolated by valves and for which the quantities of water entering and leaving can be metered. DMAs should be formed taking into account characteristics of the distribution network, the number of consumers and other factors. Measurements and analyses of flow and pressures entering/leaving the DMA, especially at night, enable more accurate calculations of the level of leaks in the DMA. This can be used to determine not only whether work should be undertaken to reduce leakage, but also to compare levels of leakage in different districts and thereby target maintenance in those areas where it will have the greatest impact. Also, DMAs enable application of pressure regulation within the zone, which would reduce water losses and decrease the number and frequency of pipe bursts.

 

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Figure 2: Components of night flow

 

The Minimal Night Flow (MNF) method is widely accepted as the best method for assessing real loss components. During the night water consumption is minimal and therefore real water losses represent a significant part of the flow entering the system/DMA. System Input Volume entering the DMA consists of water delivered to consumers and water losses. Water delivered to consumers consists of losses from service connections and night consumption, while night losses consists of similar components as given in Table 1. Components of night flow are given in Figure 2 (WSA/WCA, 1994).