What is Infrastructure Leakage Index (ILI)?
Infrastructure Leakage Index (ILI) is the ratio of current annual real losses to unavoidable annual real losses in a water distribution system. It is a performance indicator for leakage that allows fairer comparison between utilities with different network sizes, connection densities and pressures.
What it is
The ILI was developed through the International Water Association's work on water loss performance indicators. Current annual real losses, often abbreviated CARL, come from the water balance. Unavoidable annual real losses, or UARL, are calculated from network characteristics: length of mains, number of service connections, customer meter location and average operating pressure.
Because UARL reflects what is technically achievable for a given network, ILI shows how far a utility is from that level. A lower ILI means less excess leakage. ILI is dimensionless, which helps compare systems of different sizes.
Who it applies to / where it is used
ILI is used by water utilities, regulators and benchmarking programs. It appears in the AWWA M36 water audit method and in several state water loss reporting programs in the US. Check the current rule for whether your jurisdiction requires it.
How it is measured / what evidence it needs
ILI is only as good as the real loss estimate behind it, which depends on accurate system input and consumption data.
- Validated system input volume
- Billed and unbilled authorized consumption
- Apparent loss estimates
- Mains length, service connections and average pressure
- Real losses by district metered area where available
How Aqueduct helps
Aqueduct reports real losses per district metered area to feed the ILI calculation, so the number rests on measured data.
- District metered area balances through aQ WaterGuard, read from SCADA and AMI
- Night flow analysis to estimate background and burst leakage
- Pressure data trended alongside flow
- Exports for the water audit through aQ Assurance