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Table 4

IWA best practice water balance and performance indicator (originally published in Lambert & Hirner 2000)

System input volume Authorized consumption Billed authorized consumption Billed metered consumption Revenue water 
Billed unmetered consumption 
Unbilled authorized consumption Unbilled metered consumption Non-revenue water 
Unbilled unmetered consumption 
Water losses Apparent losses Unauthorized consumption 
Customer metering inaccuracies 
Real losses Leakage on transmission and/or distribution mains 
Leakage and overflows at storage tanks 
Leakage on service connections up to point of customer metering 
System input volume Authorized consumption Billed authorized consumption Billed metered consumption Revenue water 
Billed unmetered consumption 
Unbilled authorized consumption Unbilled metered consumption Non-revenue water 
Unbilled unmetered consumption 
Water losses Apparent losses Unauthorized consumption 
Customer metering inaccuracies 
Real losses Leakage on transmission and/or distribution mains 
Leakage and overflows at storage tanks 
Leakage on service connections up to point of customer metering 
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