Water balance by country · Updated 2026-09-29
Water audits in the United States: AWWA M36, state validation requirements and ILI in gallons
Running an AWWA M36-compatible water audit online: US customary units, state requirements in California, Georgia, Texas, Tennessee and Hawaii, data validity grading and how the ILI is calculated in gallons and psi.
Calculator settings for United States
- Units
- US customary: million gallons, miles, psi, $/kgal
- Benchmark category
- Standard
- Meter location
- At the house or inside — service pipe length typically 15–25 m (50–80 ft)
- Typical per-capita use
- 80–120 gal/person/day; higher in the Sun Belt
- Reporting
- AWWA M36 water audit; state programs (CA DWR/SWRCB, GA EPD, TWDB, TN, HI); validation by certified validators
In the United States the IWA water balance is known as the water audit and codified in AWWA Manual M36. A growing number of states require an annual audit: California (validated audits under SB 555 and volumetric leakage standards for larger utilities), Georgia (Water Stewardship Act), Texas (TWDB, for retail utilities and those receiving state funds), Tennessee and Hawaii among them. The AWWA Free Water Audit Software is the reference tool; this calculator produces the same indicators with guidance, saved versions and a branded report.
Running an M36 audit here
- Switch units to US customary on the Set-up step. Volumes are entered in million gallons, mains in miles, pressure in psi and cost per thousand gallons; the engine converts internally and reports both.
- Water imported goes in as a source; water exported goes in the bulk-export rows so it is excluded from customer-meter error calculations — exactly as M36 treats it.
- M36 defaults you may recognise: unauthorised consumption 0.25% of water supplied and data-handling errors 0.25% of billed metered when no better data exists. Enter them the same way here with a wide band.
- Service pipe length matters more in the US than almost anywhere: with meters at the house, 50–80 ft of customer-side pipe per connection adds substantially to the UARL. Don't leave it at zero.
Data validity vs uncertainty
M36 grades each input 1–5 and rolls it into a Data Validity Score. The ± bands in this calculator do the same job more transparently: rather than a grade, you see how each input's uncertainty propagates into real losses and the ILI. A validator can read the ranges directly.
Typical results
Validated audits across the states that publish them show median ILIs around 2–4 for larger utilities, with small systems spread widely. Real losses of 30–80 gallons per connection per day are common. California's leakage standards are set in gallons per connection per day and vary with pressure and connection density — the NRW-per-connection matrix on the results page is the same idea.