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Non-Revenue Water · Water Loss Control · IWA / AWWA Methodology · Analytics-Led
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◇ AWWA M36 · Free Water Audit Software v6.0 methodology

Water Audit Calculator.

A full water-balance audit tool. Enter system input, authorized consumption, and apparent-loss components — and we'll derive your real losses, ILI, NRW by volume and by cost, and a prioritised set of programme actions. Every input updates the balance live.

Reporting Worksheet · AWWA FWAS v6.1 methodology

Build a defensible water balance.

Inputs follow the IWA Standard Water Balance and the AWWA Free Water Audit Software v6.1 (2025) Reporting Worksheet. Each component is independently graded 1–10 — the weighted composite drives the Data Validity Score and the Priority Areas for Attention.

Self-guided audit. Step through inputs 1–5 below; results, infographics & performance indicators update live on the right. Click any ? icon for a popup explaining the field, where to find the data, and the full G1–G10 grade criteria.

1 Water supplied SIV: 0 MG/yr
Grade 5 — 50–75% sources metered; occasional accuracy testing.
Grade 5 — Monthly automated logging + review; storage changes included; data corrected on gross errors.
Grade 5 — 50–75% metered; occasional testing.
Grade 5 — Monthly automated logging by exporter; clear testing agreement.
Grade 5 — 50–75% metered; occasional testing.
Grade 5 — Monthly automated logging by selling utility; clear agreement.
2 Authorized consumption AC: 0 MG/yr
Grade 5 — ≥ 75% metered; manual reads ≥50% success; meter replacement only on failure.
Grade 5 — Metering policy with up to 20% exemptions; rough estimate of unmetered consumption.
Grade 5 — Dated procedures; low-priority reading; mixed measured + estimated.
Grade 5 — Partial documentation; formula used for known events (time × flow × count).
3 Apparent-loss components AL: 0 MG/yr
Grade 5 — Some categories documented via formula; total partly subjective.
Grade 5 — Reliable records; annual testing on small sample (<1% of inventory).
Grade 5 — Dated computerised billing; periodic limited audits.
4 Water network data ILI: —
If yes, average service-line length is automatically set to 0 and graded 10(a) per AWWA M36.
Grade 6 — Between Grade 4 and Grade 6.
Grade 6 — Between Grade 4 and Grade 6.
Grade 6 — Between Grade 4 and Grade 6.
Grade 6 — Between Grade 4 and Grade 6.
5 Cost data NRW cost: $0/yr
Grade 5 — Electronic accounting in place but data gaps known; no structured audit.
Grade 5 — Straightforward rate structure; composite from single class (e.g. residential only).
Grade 5 — Industry-standard accounting; power + treatment tracked reliably; periodic internal audit.
Infrastructure Leakage Index (ILI)
0.0
—
CARL 0 ÷ UARL 0 gal/day
NRW by volume
0.0%
—
NRW by cost
0.0%
—
Real losses
0
gal/conn·d
—
Apparent losses
0
gal/conn·d
—
Annual cost of NRW
$0
Real $0 · Apparent $0 · Unbilled $0

AWWA Standard Water Balance

Bars scale proportionally to your inputs
System Input Volume 0 MG/yr 100% of supply

Infographics

Live visualisations · update with inputs
Infrastructure Leakage Index
2 4 8 0.0
— 0 = perfect · >8 = poor
Loss composition
0% NRW
Revenue Unbilled Apparent Real
Cost of NRW · $/yr
Real
Apparent
Unbilled
$0Real · prod cost $0Apparent · retail $0Unbilled · prod cost
Service connection diagram — shows where Lp is measured
ground WATER MAIN property line curb stop Lp — utility "internal" length M meter inside building customer building
Lp measured from curb stop to the typical first point of use or customer meter.

Performance Indicators

AWWA M36 / FWAS Performance Indicators worksheet
Financial indicators
Non-Revenue Water as % by volume0.0%Headline volumetric efficiency metric
Non-Revenue Water as % by cost0.0%Apparent at retail, real at production cost
Annual cost of Apparent Losses$0Forgone retail revenue
Annual cost of Real Losses$0Production cost wasted
Annual cost of Unbilled Authorised$0Authorised but uncompensated
Operational efficiency indicators
Apparent Losses per service connection per day0 galMetering & billing accuracy
Real Losses per service connection per day (if density ≥ 32)0 galStandard metric, urban density
Real Losses per mile of mains per day (if density < 32)0 galSparse / rural systems
Real Losses per service connection per day per psi pressure0.00 galPressure-normalised
Water-loss indicators
Unavoidable Annual Real Losses (UARL)0 gal/dayTheoretical minimum at given conditions
Current Annual Real Losses (CARL)0 gal/dayFrom the water balance
Infrastructure Leakage Index (ILI)0.0CARL ÷ UARL · dimensionless
Service connection density0 /mileSwitch threshold = 32 conn/mile
Data quality
Data Validity Score0 / 100Weighted composite per AWWA
Validation Level—I (Limited) → V (Excellent)
Authorized Consumption 0 MG/yr 0% of supply
Water Losses 0 MG/yr 0% of supply
Billed Authorized 0 MG/yr
Unbilled 0 MG/yr
Apparent 0 MG/yr
Real 0 MG/yr
Revenue Water Non-Revenue Water (NRW)

Data Validity Score

Weighted composite per AWWA M36
50 / 100 — Validation Level III · Moderate

Suitable for internal benchmarking. Improving the highest-impact lowest-graded inputs first will raise the composite fastest.

Priority Areas for Attention

Top three weight-adjusted improvements

    Programme priorities

    Based on the result values themselves

      Loss Control Planning Guide

      Validation-level-driven · per AWWA M36 guidance
      Current state
      —

      Recommended programme stage

      Adjust the inputs and grades above to see tailored planning guidance.

        AI Tools · Google Gemini (free tier · BYO key)

        Generate narratives & ask questions about your audit.

        Generate audit narrative

        Produces a leadership-ready prose summary of the current audit — headline finding, cost picture, operational priorities, and a short data-quality close. Uses your current input values and grades.

        No narrative yet. Click Generate to produce one based on the current audit.

        Ask the auditor

        Ask a question about your current audit — e.g. "What's driving the high apparent losses?" or "Should we prioritise pressure management or meter testing?" The AI answers with values from your current numbers.

        ADefinitions & GlossaryClick to expand · AWWA M36 / IWA Water Loss Specialist Group terms
        System Input Volume (SIV)
        Total annual water entering the distribution system from all sources — own production + imports − exports. The denominator of most performance indicators.
        Authorized Consumption
        All water use permitted by the utility, whether billed or unbilled, metered or unmetered. The sum of billed authorized (revenue water) and unbilled authorized (NRW).
        Billed Authorized Consumption
        Authorized water use that the utility bills (metered or flat-rate). Equals Revenue Water.
        Unbilled Authorized Consumption
        Authorized water use that the utility does not bill — e.g. firefighting, hydrant flushing, mains scouring, municipal-building exemptions.
        Water Losses
        System Input Volume minus Authorized Consumption. Split into Apparent and Real Losses.
        Apparent Losses
        Non-physical losses: unauthorized consumption, customer-meter under-registration, and systematic data-handling errors. Cost the utility at the retail tariff.
        Real Losses
        Physical losses from the pressurised system: mains leakage, service-line leakage, and leakage/overflow at storage. Cost the utility at variable production cost.
        Non-Revenue Water (NRW)
        Water Losses + Unbilled Authorized Consumption. The portion of supply that does not generate retail revenue.
        Revenue Water
        Billed Authorized Consumption — the portion of supply that does generate retail revenue.
        Unavoidable Annual Real Losses (UARL)
        The theoretical minimum real losses for a well-managed system at a given pressure, density, and configuration. AWWA US-units formula: (5.41·Lₘ + 0.15·Nc + 7.5·Lp) × P, in gallons per day.
        Current Annual Real Losses (CARL)
        The actual annual real-loss volume computed from the water balance.
        Infrastructure Leakage Index (ILI)
        CARL ÷ UARL. A dimensionless efficiency ratio: 1.0 means real losses are at the theoretical minimum; higher values mean more recoverable leakage.
        Service Connection Density
        Connections per mile of mains. Below 32 conn/mile, AWWA recommends benchmarking real losses per mile of mains rather than per connection.
        Customer Retail Unit Cost (CRUC)
        Composite retail rate ($/1000 gal) applied to Apparent Losses, because that revenue is forgone at the retail tariff. Should be weighted across all customer classes.
        Variable Production Cost
        Marginal cost ($/1000 gal) of producing/treating/pumping one additional unit of water — applied to Real Losses, because that water is physically wasted.
        Data Validity Score
        Composite 0–100 score reflecting the weighted quality of all audit inputs. Drives the Validation Level (I–V) and the Priority Areas for Attention.
        Validation Level
        I (≤30): Limited; II (31–50): Basic; III (51–70): Moderate; IV (71–90): Strong; V (91–100): Excellent. Indicates the appropriate uses of the audit result.
        Leakage Emissions Initiative (LEI)
        AWWA Water Loss Control Committee 2025 methodology that converts real losses to embedded CO₂ emissions (treatment + pumping energy × grid emissions factor). Integrated as the Carbon Balance in FWAS v6.1.
        BGrading MatrixClick to expand · Criteria for grades 1–10 across every input

        Grading is independently applied to each input. Odd grades (1, 3, 5, 7, 9) indicate "conditions between" the adjacent even-grade bands. The weighted composite of these gradings produces the Data Validity Score.

        Volume from own sources weight 10 · n/a allowed
        G1< 25% of sources metered; estimates dominate; no testing.
        G2Between Grade 1 and Grade 2.
        G325–50% sources metered; remainder estimated; no testing.
        G4Between Grade 2 and Grade 4.
        G550–75% sources metered; occasional accuracy testing.
        G6Between Grade 4 and Grade 6.
        G7≥ 75% sources metered (or ≥ 90% of flow from meters); annual testing; <25% outside ±6%.
        G8Between Grade 6 and Grade 8.
        G9100% sources metered; annual testing; <10% outside ±6%.
        G10100% sources metered; semi-annual testing; <10% outside ±3%; third-party-reviewed procedures.
        Own-sources master-meter error adjustment weight 4
        G1Crude paper records; data error cannot be determined.
        G2Between Grade 1 and Grade 2.
        G3Daily manual readings; no tank-elevation balancing; archived data adjusted only on gross errors.
        G4Between Grade 2 and Grade 4.
        G5Monthly automated logging + review; storage changes included; data corrected on gross errors.
        G6Between Grade 4 and Grade 6.
        G7Weekly review of hourly automated data; tank changes included; gross errors corrected.
        G8Between Grade 6 and Grade 8.
        G9Daily review of continuous logged data; gaps corrected daily.
        G10SCADA-balanced flows; daily review; calibrations between SCADA and source meters.
        Water imported weight 5 · n/a allowed
        G1< 25% of imports metered; estimates dominate; no testing.
        G2Between Grade 1 and Grade 2.
        G325–50% metered; no testing.
        G4Between Grade 2 and Grade 4.
        G550–75% metered; occasional testing.
        G6Between Grade 4 and Grade 6.
        G7≥ 75% metered; annual testing; <25% outside ±6%.
        G8Between Grade 6 and Grade 8.
        G9100% metered; annual testing; <10% outside ±6%.
        G10100% metered; semi-annual testing; <10% outside ±3%.
        Imported master-meter error adjustment weight 3 · n/a allowed
        G1Paper records incomplete; vague written agreement.
        G2Between Grade 1 and Grade 2.
        G3Daily manual readings; vague testing provisions in agreement.
        G4Between Grade 2 and Grade 4.
        G5Monthly automated logging by exporter; clear testing agreement.
        G6Between Grade 4 and Grade 6.
        G7Weekly review of hourly data by exporter; gaps corrected weekly.
        G8Between Grade 6 and Grade 8.
        G9Daily review of continuous data by exporter.
        G10SCADA-logged; daily review; contract reviewed at least every 5 years.
        Water exported weight 3 · n/a allowed
        G1< 25% of exports metered; no testing.
        G2Between Grade 1 and Grade 2.
        G325–50% metered; no testing.
        G4Between Grade 2 and Grade 4.
        G550–75% metered; occasional testing.
        G6Between Grade 4 and Grade 6.
        G7≥ 75% metered; annual testing; <25% outside ±6%.
        G8Between Grade 6 and Grade 8.
        G9100% metered; annual testing; <10% outside ±6%.
        G10100% metered; semi-annual testing; <10% outside ±3%.
        Exported master-meter error adjustment weight 2 · n/a allowed
        G1Paper records incomplete; vague written agreement with importer.
        G2Between Grade 1 and Grade 2.
        G3Daily manual readings; vague testing provisions.
        G4Between Grade 2 and Grade 4.
        G5Monthly automated logging by selling utility; clear agreement.
        G6Between Grade 4 and Grade 6.
        G7Weekly review of hourly data; data gaps corrected weekly.
        G8Between Grade 6 and Grade 8.
        G9Daily review of continuous data; daily gap correction.
        G10SCADA-logged; daily review; contract reviewed every 5 years.
        Billed metered weight 10 · n/a allowed
        G1< 50% of customers metered; flat-rate dominates.
        G2Between Grade 1 and Grade 2.
        G3≥ 50% metered; manual reads <50% success; no meter testing.
        G4Between Grade 2 and Grade 4.
        G5≥ 75% metered; manual reads ≥50% success; meter replacement only on failure.
        G6Between Grade 4 and Grade 6.
        G7≥ 90% metered; ≥80% read success; basic accuracy testing.
        G8Between Grade 6 and Grade 8.
        G9≥ 97% metered; ≥90% read success; routine accuracy testing & replacement.
        G10≥ 99% metered; ≥95% read success (AMR/AMI); annual + 3-yr third-party billing audits.
        Billed unmetered weight 3 · n/a allowed
        G1Flat-fee billing throughout; consumption estimated from fixture counts.
        G2Between Grade 1 and Grade 2.
        G3Flat-fee billing with some sample-metered areas extrapolated.
        G4Between Grade 2 and Grade 4.
        G5Metering policy with up to 20% exemptions; rough estimate of unmetered consumption.
        G6Between Grade 4 and Grade 6.
        G7Metering policy with up to 15% exemptions; grouped estimate per audit.
        G8Between Grade 6 and Grade 8.
        G9< 5% unmetered; site-specific estimates per account.
        G10< 2% unmetered; programme to minimise exceptions; site-specific estimates.
        Unbilled metered weight 2 · n/a allowed
        G1No written exemption policy; no reliable account count.
        G2Between Grade 1 and Grade 2.
        G3Scattered written directives; sporadic meter reading.
        G4Between Grade 2 and Grade 4.
        G5Dated procedures; low-priority reading; mixed measured + estimated.
        G6Between Grade 4 and Grade 6.
        G7Written policy in place; reliable municipal-building reads; sporadic elsewhere.
        G8Between Grade 6 and Grade 8.
        G9Annual reading for audit; high-level billing audit confirms account census.
        G10Clear policy; annual reading; regular auditing; minimum exempt accounts.
        Unbilled unmetered weight 1
        G1Total volume purely subjective; no policy or recordkeeping.
        G2Between Grade 1 and Grade 2.
        G3Random documentation of events; no quantified total.
        G4Between Grade 2 and Grade 4.
        G5Partial documentation; formula used for known events (time × flow × count).
        G6AWWA default in use — 1.25% of System Input Volume.
        G7Policies for some categories; reasonable inference; subjective for unsupervised use.
        G8Between Grade 6 and Grade 8.
        G9Mostly quantified via formula or temporary meters; some subjectivity remains.
        G10Clear policies; minimised authorised unbilled use; all events recorded and quantified.
        Unauthorized consumption weight 1
        G1Unknown extent; purely subjective.
        G2Between Grade 1 and Grade 2.
        G3Known to occur; periodic field reports; total approximated.
        G4Between Grade 2 and Grade 4.
        G5Some categories documented via formula; total partly subjective.
        G6AWWA default in use — 0.25% of water supplied.
        G7Coherent policy for major categories; inferred from records.
        G8Between Grade 6 and Grade 8.
        G9Combination of formula-quantified events and subjective estimates for unconfirmed use.
        G10Clear policy; enforcement staff; every event recorded and quantified.
        Customer metering inaccuracy weight 5 · n/a allowed
        G1Disorganised paper records; no testing or replacement programme; loss estimated.
        G2Between Grade 1 and Grade 2.
        G3Improving recordkeeping; testing only on customer request.
        G4Between Grade 2 and Grade 4.
        G5Reliable records; annual testing on small sample (<1% of inventory).
        G6Between Grade 4 and Grade 6.
        G7Electronic records; mix of new + dated meters; routine but limited testing.
        G8Between Grade 6 and Grade 8.
        G9Ongoing replacement + testing; samples of varying age & throughput; volume well-quantified.
        G10Statistically significant testing programme; new metering tech embraced; third-party reviewed.
        Systematic data-handling errors weight 2
        G1Vague account-activation procedures; paper billing records; no audit.
        G2Between Grade 1 and Grade 2.
        G3Procedures exist but need refinement; sporadic internal audits.
        G4Between Grade 2 and Grade 4.
        G5Dated computerised billing; periodic limited audits.
        G6Default value (0.25% of billed) in use — adequate procedures with annual checks.
        G7Reviewed procedures; computerised billing with reports; annual internal checks.
        G8Between Grade 6 and Grade 8.
        G9Biannual procedure review; routine reports; 5-yr third-party billing audit.
        G10Robust written policy; high-functionality billing system; 3-yr third-party audit.
        Length of mains weight 5
        G1Poor paper as-built records; length is a guess.
        G2Between Grade 1 and Grade 2.
        G3Paper records in uncertain condition; no annual install/abandonment tracking.
        G4Between Grade 2 and Grade 4.
        G5Written commissioning procedures exist but gaps remain.
        G6Between Grade 4 and Grade 6.
        G7Sound procedures; either accurate paper records with field validation, or maintained electronic records.
        G8Between Grade 6 and Grade 8.
        G9GIS / asset-management system in good condition.
        G10GIS + asset-management agreement; random field validation; annual review.
        Active + inactive service connections weight 5
        G1Vague permitting; poor paper records; count may be 10–15% in error.
        G2Between Grade 1 and Grade 2.
        G3General policy + paper records; count may be 5–10% in error.
        G4Between Grade 2 and Grade 4.
        G5Written activation procedures; transitioning to electronic system; up to 5% error.
        G6Between Grade 4 and Grade 6.
        G7Electronic system with annual install/abandon totals; limited field checks; ≤3% error.
        G8Between Grade 6 and Grade 8.
        G9Well-managed electronic system; biannual procedure review; ≤2% error.
        G10Billing, info-system, and GIS counts agree; field-validated; <1% error.
        Avg. length of customer service line (curb to meter) weight 3
        G1Vague ownership policy; curb stops poorly documented; length is arbitrary.
        G2Between Grade 1 and Grade 2.
        G3Policy defines curb stop as boundary; locations not well documented.
        G4Between Grade 2 and Grade 4.
        G5Good policy; reasonably documented; average estimate from limited paper records.
        G6Between Grade 4 and Grade 6.
        G7Clear written policy; accurate paper or basic electronic records; periodic field checks.
        G8Between Grade 6 and Grade 8.
        G9Curb stops/meters standardised and inspected; accurate electronic records.
        G10Either (a) meters at curb stop — value = 0; or (b) GIS-based with statistical field validation.
        Average operating pressure weight 5
        G1Crude paper records of pump characteristics; pressure is a guess.
        G2Between Grade 1 and Grade 2.
        G3Limited telemetry; handwritten logs; pressure data only when complaints arise.
        G4Between Grade 2 and Grade 4.
        G5Pressure-zone controls in place; some basic telemetry logging.
        G6Between Grade 4 and Grade 6.
        G7Reliable zone separation; well-covered telemetry monitoring across the system.
        G8Between Grade 6 and Grade 8.
        G9Well-managed zones; full-scale SCADA monitoring with representative real-time pressure data.
        G10SCADA + hydraulic model; very precise pressure data; annual calibration.
        Total annual cost of operating water system weight 3
        G1Incomplete paper records; calculation is a guess.
        G2Between Grade 1 and Grade 2.
        G3Incomplete paper or electronic records; majority of costs estimated.
        G4Between Grade 2 and Grade 4.
        G5Electronic accounting in place but data gaps known; no structured audit.
        G6Between Grade 4 and Grade 6.
        G7Industry-standard accounting; all costs tracked; periodic internal audit (not CPA).
        G8Between Grade 6 and Grade 8.
        G9Industry-standard accounting; annual internal audit + 3-yr third-party CPA.
        G10Industry-standard accounting; annual internal + annual third-party CPA audit.
        Customer retail unit cost weight 5 · n/a allowed
        G1Cumbersome inconsistent rate structure; degree of error undetermined.
        G2Between Grade 1 and Grade 2.
        G3Dated rate structure; composite rate roughly estimated.
        G4Between Grade 2 and Grade 4.
        G5Straightforward rate structure; composite from single class (e.g. residential only).
        G6Between Grade 4 and Grade 6.
        G7Current rate structure; weighted-average composite from residential block rates.
        G8Between Grade 6 and Grade 8.
        G9Weighted composite across residential, commercial, industrial, institutional classes.
        G10Current effective rate; 5-yr third-party review of composite-rate methodology.
        Variable production cost weight 5
        G1Incomplete paper records of power + treatment costs; unit cost is a guess.
        G2Between Grade 1 and Grade 2.
        G3Reasonable but incomplete records; rough estimate of unit variable cost.
        G4Between Grade 2 and Grade 4.
        G5Industry-standard accounting; power + treatment tracked reliably; periodic internal audit.
        G6Between Grade 4 and Grade 6.
        G7All variable production costs tracked, including secondary costs (residuals, wear, expansion); annual internal audit.
        G8Between Grade 6 and Grade 8.
        G9Primary + secondary costs tracked; annual internal + 3-yr third-party knowledgeable review.
        G10Either annual third-party CPA audit OR fully bulk-imported supply with audited unit cost.
        CCarbon Balance v6.1 · 2025Click to expand · LEI-methodology emissions from real losses

        FWAS v6.1 (2025) integrates the AWWA Water Loss Control Committee Leakage Emissions Initiative (LEI) methodology to convert real losses into embedded greenhouse-gas emissions. Treated water that leaks carries the energy and chemicals used to produce it — so reducing real losses also reduces avoidable emissions.

        Typical US range 1,000–3,000 kWh/MG; pumped systems sit higher. Use the audited variable-energy figure if available.
        US national average ≈ 0.39 kg CO₂e/kWh (eGRID). Use your local grid factor where available.
        Embedded emissions from coagulants, disinfectants, and process chemicals. Typical surface-water plants 80–200 kg CO₂e/MG.
        Real-loss energy
        0 MWh/yr
        Avoidable CO₂e from real losses
        0 t CO₂e/yr
        Equivalent
        0 US cars/yr

        Calculation: (Real losses MG/yr × energy kWh/MG × emissions kg/kWh ÷ 1000) + (Real losses MG/yr × chemicals kg/MG ÷ 1000). Vehicle equivalence based on US EPA passenger-vehicle average of 4.6 t CO₂e/yr.

        Methodology. This tool implements the IWA Standard Water Balance and the AWWA M36 / Free Water Audit Software v6.1 (2025) Reporting Worksheet component definitions and grading framework. Defaults follow AWWA convention: unauthorized consumption 0.25% of System Input Volume; unbilled unmetered 1.25% of SIV; systematic data-handling errors 0.25% of billed. Unavoidable Annual Real Losses follow the AWWA US-unit formula UARL (gal/day) = (5.41·Lm + 0.15·Nc + 7.5·Lp) × P, where Lm = miles of mains, Nc = service connections, Lp = total length of customer service lines (curb-to-meter, in miles), and P = average operating pressure (psi). Infrastructure Leakage Index = CARL / UARL. The Data Validity Score is a weighted composite where input weights approximate each component's typical contribution to total volume or cost; results map to Validation Levels I (Limited) through V (Excellent). Carbon Balance follows the AWWA Water Loss Control Committee Leakage Emissions Initiative (LEI) methodology integrated in FWAS v6.1. All grading-criteria text is paraphrased from the AWWA published Grading Matrix; refer to the AWWA M36 Manual and FWAS for the authoritative original. The AWWA Water Audit Compiler is available to assemble multi-utility or multi-year audits. Results illustrative — a validated audit replaces these with measured values.

        Want a validated version of these numbers?

        A formal AWWA audit replaces estimates with measured, validated values you can act on and report.

        Start an audit See the methodology
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