Learn

Short, practical explanations of the terms behind every number in the calculator.

• Non-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.

• The IWA water balance explained: every component, with a worked example

  A plain-language walk through the IWA standard water balance table — system input, authorised consumption, apparent losses, real losses, revenue and non-revenue water — with the formulas, a worked example and the mistakes that trip people up.

• Real losses vs apparent losses: the difference, and why it decides your strategy

  Real losses are leaks; apparent losses are metering, theft and billing failures. They are found differently, valued differently and fixed differently. Here's how to tell them apart and where to spend first.

• Litres per connection per day: the leakage indicator that replaces NRW percent

  Why the IWA recommends real losses in litres per service connection per day (when the system is pressurised), how to calculate it, what 'w.s.p.' means, and how it compares across pressures and supply regimes.

• Minimum night flow and district metered areas: the bottom-up check on your water balance

  A top-down water balance estimates real losses as a residual. Minimum night flow analysis in district metered areas measures them directly. How MNF works, how to net off legitimate night use, and how to reconcile the two methods.

• How to reduce non-revenue water: a strategy built from the water balance

  An NRW reduction strategy that follows the numbers: value each component, pick the interventions with the shortest payback, set targets in the right units, and measure progress. Covers pressure management, active leakage control, meter replacement, billing clean-up and intermittent supply.

• WB-EasyCalc online: a free web alternative to the Excel water balance

  WB-EasyCalc has been the standard free water balance spreadsheet since 2006. WaterBalanceCalc implements the same IWA methodology in the browser, imports your existing EasyCalc files, and adds guidance, saved versions and branded reports.

• AWWA M36 water audit: how to calculate ILI and validated water loss in the US

  The AWWA M36 water audit uses the IWA water balance with US terminology, gallons and psi. How the audit is structured, how data validity grading works, what state regulators expect, and how to run one online.