The AWWA M36 water loss audit: a guide for utilities and cities.
An AWWA M36 audit balances all the water a utility puts into its system against authorized use, apparent losses and real losses. A live balance keeps those volumes measured all year instead of rebuilt at filing time.
The lines of the audit.
| Line | What it covers | What a live balance supplies |
|---|---|---|
| System input volume | Water produced or imported, less exports | Continuous volumes per source and district |
| Billed authorized consumption | Metered and unmetered billed use | AMI reads summed per district |
| Unbilled authorized consumption | Firefighting, flushing, some municipal use | Metered use at municipal sites |
| Apparent losses | Meter error, theft and data errors | Meters reading outside their usual range |
| Real losses | Leakage from mains, services and storage | Night flow per district, showing where loss sits |
State filing rules.
| Rule or standard | Date | What it asks for |
|---|---|---|
| Texas, 31 TAC 358.6 | Annually by 1 May | Utilities with more than 3,300 connections |
| Texas, all retail suppliers | Every five years; next due 1 May 2026 | Annual audits validated within 90 days since 2025 |
| Georgia, Rule 391-3-33 | Annually by 1 March | Systems serving 3,300 or more people, IWA and AWWA method |
| AWWA Free Water Audit Software | v6.1, 2025 | Standard balance; the new version adds carbon calculations |
Why audits get hard.
Volumes gathered once a year
Inputs rebuilt from scattered systems at the deadline
A total, not a location
Real losses known for the system, not the district
Validation turns into reconstruction
Data validity grades drop when records are thin
Sources4 references cited on this page
Related
Common questions
Real losses are water that physically escapes the pipes, through breaks, leaking service connections and tank overflows. Apparent losses are water that reaches customers but is not correctly measured or billed. In the AWWA M36 balance, real losses are what remains once authorized use and apparent losses are counted.
No. Aqueduct supplies measured volumes per source and district and points to the district where leakage is concentrated. Your team or qualified validator completes the audit in the AWWA Free Water Audit Software and files it with the state on its deadline.
By replacing estimated inputs with measured ones. Calibrated production meters, AMI totals for the same period and checked master meter error each lift the grade of an input. Aqueduct keeps those volumes current all year and flags meters reading out of range. See AWWA M36.
No. The annual audit is still the filing. A live balance keeps the inputs measured between audits and shows which district metered area holds the loss, so crews act in month two instead of after the filing. See non-revenue water.
See Aqueduct on your own facility.
Bring a site, a utility bill or a question. We will show you where the loss is.