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 |