Every IWA component with honest uncertainty
System input, billed and unbilled consumption, unauthorised use, meter under-registration, data errors — and real losses as the residual, each with a ±95% band you can defend.
Free · IWA standard · No sign-up to run one
Your water balance, done properly, in ten minutes.
Non-revenue water, real and apparent losses, the Infrastructure Leakage Index, the cost of leakage and its carbon — with uncertainty bands, an assistant for the numbers you don't have, and a report you can send.
- ✓ Imports WB-EasyCalc files
- ✓ Metric or US units
- ✓ PDF, Excel, email, share
Worked example22,700,000 m³/year into supply
System input volume
Authorised consumption
Water losses
Billed authorised
Unbilled authorised
Apparent losses
Real losses
Billed metered
Billed unmetered
Unbilled metered
Unbilled unmetered
Unauthorised consumption
Meter inaccuracies & data errors
Real losses
Revenue water
Non-revenue water
Enter a system input volume and the ledger starts filling in.
- NRW
- 29.3%
- ILI
- 3.07 B
- Real losses
- ±10%
Fills in as you type. Hatching shows the 95% confidence band.
What you get
Swipe →
How it works
- 1
Water in
Each source, its volume and meter accuracy. Pick a treatment category and the carbon factor is applied.
- 2
Consumption and losses
Billed and unbilled use from billing; estimates for illegal use and meter under-reading — with help if you need it.
- 3
Network and pressure
Mains, connections, service-pipe length and zone pressures set the unavoidable leakage for your system.
- 4
Results
The balance in m³ and tCO₂, the indicators, the bands, the cost, what-if levers and a findings narrative for the board.
Missing a number? Ask.
Most balances stall on meter under-registration, illegal connections, service-pipe length or marginal cost. Beside each of those inputs is Help me estimate: tell the assistant what you know and it proposes a value, a ± band and the reason — grounded in what is typical for your country and system. Accept it with one tap.
When you're done, it drafts the findings for your report. Every accepted value stays visible in the inputs appendix.
What meter under-registration should I assume? Regional Queensland council, boundary meters, ~30% of meters over 12 years old.
For an Australian regional scheme with boundary metering and an ageing fleet, 4% is a reasonable start: 10–15-year-old mechanical meters typically test at 3–6% under-registration, driven by low-flow losses on 20 mm meters. Carry ±40% until you have bench-test data.
Use 4% ± 40%
Where you are changes the answer
Reporting rules, metering practice and typical results differ by country. These guides give the settings to use and what to expect.
Understand the numbers
All 13 guidesNon-revenue water (NRW): what it is and how to calculate it
NRW is the water a utility puts into supply but never bills. Learn the IWA definition, the formula, what counts as apparent versus real losses, and why percentages mislead.
Infrastructure Leakage Index (ILI) explained
The ILI compares your current real losses with the unavoidable minimum for your network. Learn the formula, the World Bank bands from A1 to D, and what your ILI tells you to do next.
The UARL formula: unavoidable annual real losses
UARL = (18 × Lm + 0.8 × Nc + 25 × Lp) × P. What each term means, where the coefficients come from, and how supply time and pressure change the answer.
Apparent losses: meter under-registration, illegal use and data errors
Apparent losses are water consumed but never recorded. How to estimate customer meter under-registration, unauthorised consumption and billing data errors for a water balance.
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.
The carbon footprint of leakage and non-revenue water
Every cubic metre lost to leakage carries the energy and chemicals it took to treat and pump it. How to estimate the tCO₂ embodied in real losses using treatment-process carbon factors.
Questions people ask
What is a water balance?
A water balance accounts for every cubic metre put into a distribution system over a period: what customers used (billed and unbilled, metered and unmetered), what was lost to leakage (real losses) and what was consumed but never recorded (apparent losses). The IWA standard water balance is the internationally accepted format.
How is non-revenue water (NRW) calculated?
NRW = system input volume − billed authorised consumption. It includes unbilled authorised consumption, apparent losses and real losses. This calculator reports NRW as a volume, as a percentage of input, per service connection per day, and as an annual cost.
What is the Infrastructure Leakage Index (ILI)?
ILI = current annual real losses ÷ unavoidable annual real losses (UARL). The UARL is the technically achievable minimum leakage for your network's length of mains, number of connections, service pipe length and average pressure. An ILI of 1 is world class; above 8 means leakage reduction is urgent.
Is this the same as WB-EasyCalc?
It implements the same IWA methodology — the standard water balance with 95% confidence limits, the Lambert UARL formula, the World Bank Institute performance bands and a carbon balance by treatment process — as a web app with guidance built in. You can import an existing WB-EasyCalc or WCB-EasyCalc workbook.
How does the AI assistant help?
Beside each hard-to-source input is a 'Help me estimate' button. The assistant proposes a value with an uncertainty band and a one-line justification, using what is typical for your country, climate and system type. It can also draft a structured findings summary. Suggestions are starting points and are always visible in the report's inputs appendix.
Is it really free?
Yes. The calculator, saving, PDF and Excel export, sharing and the AI assistant are free. Creating an account lets you save balances, keep versions and share them with colleagues.
Does it work in US gallons?
Yes. Switch to US customary units and enter million gallons, miles and psi. Calculations follow the same IWA / AWWA M36-compatible top-down approach.