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

Non-revenue water is reduced by a sequence, not a single project. The water balance tells you the size and value of each component; the performance indicators tell you how far from the achievable minimum you are; the economics tell you where to spend first. Here is the sequence that works.

1. Establish the balance and its uncertainty

Run the full IWA balance with honest ± bands. If the real-loss band is wider than ±30%, spend first on data: bulk meter calibration, a billing audit, a customer meter test programme and a sample of DMAs for night-flow measurement. Money spent narrowing the balance is rarely wasted, because it decides everything after it.

2. Value the components

Apparent losses at tariff, real losses at marginal cost (or tariff for the sellable share), unbilled authorised at whichever applies. Rank by annual value. In most systems apparent losses are worth more per cubic metre and real losses more in total; the ranking decides the order of the programme.

3. Quick wins on apparent losses

• Test a stratified sample of customer meters by age and size; replace the classes that under-read most (often large meters on low-flow customers, and any mechanical meter past 10–12 years).
• Audit the billing database against the customer register and the GIS: unbilled accounts, meters with no account, accounts with no meter, long-running estimated reads.
• Target unauthorised use where the survey data points: bypasses at large customers first, then illegal domestic connections in the highest-risk areas.

4. Pressure management

Leakage varies with pressure to a power of roughly 1.0 to 1.5 (the N1 exponent). Reducing average pressure by 20% in a zone typically cuts leakage there by 20–30% and halves the burst rate, for the cost of a pressure-reducing valve and a chamber. Use the calculator's what-if lever to see the system-wide effect before you design zones.

5. Active leakage control

Set up DMAs, log night flows and survey the areas with the highest excess flow using acoustic correlation or noise loggers. Target the economic level of leakage: keep surveying until the marginal cost of finding the next leak exceeds the value of the water it is losing. Speed of repair matters as much as detection — a leak's volume is its flow rate multiplied by how long it runs.

6. Targets in the right units

Set targets as litres per connection per day (w.s.p.), an ILI band, and value of NRW as a share of operating cost. Avoid a bare NRW percentage as the headline target: it is diluted by consumption growth and inflated by drought restrictions, and it invites the wrong behaviour.

7. Intermittent supply

In intermittently supplied systems the sequence changes. Restoring continuous supply zone by zone — with pressure management to keep leakage in check — often reduces real losses per connection even though hours of supply rise, because filling and draining the network each day causes bursts and pulls contamination in. Express everything w.s.p. so that progress is visible during the transition.

8. Measure every year

Repeat the balance annually with the same definitions and compare in volume-based indicators. Save each year as a version so the trend is visible and the uncertainty bands narrow as data quality improves.