Water balance by country · Updated 2026-09-29
Leakage and the water balance in England and Wales: Ofwat, Ml/d, MLE and the 50% by 2050 target
How UK water companies build the annual water balance for Ofwat reporting, reconcile top-down and bottom-up leakage with MLE, and how the IWA balance and ILI map onto the Ml/d and litres-per-property measures used in England and Wales.
Calculator settings for United Kingdom
- Units
- Metric — leakage reported in Ml/d and litres/property/day
- Benchmark category
- Standard
- Meter location
- Boundary (external meters) or inside; ~40–50% of households still unmeasured
- Typical per-capita use
- 130–150 L/person/day
- Reporting
- Ofwat annual performance reporting (England & Wales); WICS / Scottish Water (Scotland); NI Water (Northern Ireland)
The United Kingdom is where much of the IWA water-balance methodology was developed — the BABE concepts, the UARL formula and the economic level of leakage all have their roots in UK research in the 1990s. Today every company in England and Wales reports leakage annually to Ofwat as a three-year average in megalitres per day, with a sector commitment to halve leakage from 2017–18 levels by 2050.
How the UK balance is built
Companies reconcile a top-down water balance with a bottom-up estimate from district metered area night flows using maximum likelihood estimation (MLE), which weights each side by its uncertainty. This calculator delivers the top-down half with explicit uncertainty bands, which is what MLE needs. Enter unmeasured household consumption from your per-capita monitor with its confidence band — with 40–50% of households still unmeasured, this is the largest uncertainty in most UK balances.
Mapping the measures
| UK measure | In this calculator |
|---|---|
| Leakage (Ml/d) | Real losses per day ÷ 1,000 |
| Leakage (litres/property/day) | Real losses per connection per day (w.s.p.) — properties ≈ connections |
| Per capita consumption (l/h/d) | Billed + unbilled household consumption ÷ population |
| Distribution input | System input volume |
| Non-household consumption | Billed metered (non-domestic category) |
Local specifics
- Meters where present are usually external boundary boxes; enter 0–3 m of service pipe. Older internal meters warrant 5–10 m.
- Supply-pipe leakage (customer side of the boundary) is reported within total leakage in England and Wales; include it in real losses for consistency with Ofwat.
- Treatment is 'traditional' for most surface and groundwater works; note that carbon reporting for leakage increasingly features in company net-zero routemaps.
Typical results
England and Wales companies report roughly 60–120 litres per property per day, corresponding to ILIs of about 1.5 to 3 at typical pressures — good by world standards, with the frontier companies in band A2. Scottish Water and NI Water report on similar bases through their own regulators.