Learn · Updated 2026-09-29
Water audit vs water balance: IWA and AWWA M36 compared
The IWA water balance and the AWWA M36 water audit are the same idea with different vocabulary. Here's how the terms map and how to move between them.
If you work in North America you probably say 'water audit' and use AWWA Manual M36. Almost everywhere else the term is 'water balance' after the International Water Association. The underlying method — a top-down accounting of every cubic metre with 95% confidence limits — is the same, and M36 explicitly adopts the IWA balance and the ILI.
| IWA term | AWWA M36 term | Notes |
|---|---|---|
| System input volume | Water supplied | M36 splits into volume from own sources and water imported, less water exported |
| Real losses | Real losses | Identical |
| Apparent losses | Apparent losses | Identical; World Bank uses 'commercial losses' |
| Unavoidable annual real losses (UARL) | UARL | Same Lambert formula |
| Infrastructure Leakage Index | ILI | Identical |
| Litres/connection/day | Gallons/connection/day | Unit conversion only |
| Average pressure (m) | Average pressure (psi) | 1 m ≈ 1.42 psi |
Using this calculator for an M36-style audit
Switch the units to US customary and enter million gallons, miles and psi. Water exported goes in the bulk export rows so it is excluded from customer meter error calculations. The results include gallons per connection per day and the ILI, alongside the IWA volume-based indicators.
What M36 adds
M36 includes a data validity grading (1–5 for each input) that rolls up into a data validity score. The uncertainty bands in this calculator serve the same purpose more directly: instead of a grade, you carry an explicit ± on each input and see it propagate into the real-loss figure.
Put it into practice
Run your own water balance and see these indicators for your system — free, in about ten minutes.
Start a water balance