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The amount of water leakage contributing to the water losses for the selected supply zone was determined from the South African Night Flow Analysis Model (SANFLOW version 2.03). The model was developed by the South African Water Research Commission in order to determine real losses in a particular supply zone using the recorded minimum night flows (MNFs) as the major input (McKenzie 1999). Water leakage was estimated as the system's excess night flow (ENF) by subtracting the expected minimum night flow (EMNF) from the measured MNF. According to McKenzie (1999), the MNF is the lowest flow into the District Metered Area (DMA) over a 24-hour period, which generally occurs between 12 am and 4 am when most consumers are inactive. Table 1 presents the components of night flows.

Table 1

Components of the night flow (McKenzie 1999)

Components of night flowCompositionAbbreviationUnitMethod of determination
EMNF Domestic users Qdom (L/h) Estimated 
Small non-domestic users Qbulk,small (L/h) Estimated 
Large non-domestic users Qbulk, large (L/h) Measured 
Transfer Transfer of water to neighboring zones Qtrans (L/h) Measured 
ENF Background losses Qloss,BG (L/h) Estimated 
Burst pipes Qloss,B (L/h) Calculated 
Components of night flowCompositionAbbreviationUnitMethod of determination
EMNF Domestic users Qdom (L/h) Estimated 
Small non-domestic users Qbulk,small (L/h) Estimated 
Large non-domestic users Qbulk, large (L/h) Measured 
Transfer Transfer of water to neighboring zones Qtrans (L/h) Measured 
ENF Background losses Qloss,BG (L/h) Estimated 
Burst pipes Qloss,B (L/h) Calculated 

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