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

Ask an experienced water loss practitioner how leaky a system is and they will not answer in percent. They will answer in litres per service connection per day — the volume-based indicator the IWA recommends for real losses and for non-revenue water in systems with more than about 20 connections per kilometre of mains.

The formula

'w.s.p.' means 'when the system is pressurised'. Leakage only occurs while there is pressure, so a system supplied 12 hours a day is compared on the same footing as one supplied 24 hours. For continuous supply the correction is 1.

Why connections and not kilometres

In most urban networks the majority of leakage is on service connections, not mains, so losses scale with the number of connections rather than pipe length. Below about 20 connections per km (rural trunk systems) the IWA recommends litres per km of mains per day instead. The calculator reports both, plus losses per connection per metre of pressure for very small systems where the ILI is unreliable.

What good looks like

Typical values: under 50 L/conn/day at 40 m pressure is world class; 100–200 is common in well-managed European and Australian utilities; 300–600 is typical of systems with ageing infrastructure or limited leakage control; above 1,000 is found in many low-income intermittent-supply systems. Because leakage rises with pressure, the World Bank Institute matrix gives thresholds by average pressure — the calculator places your result in the right column automatically.

NRW per connection

The same indicator applies to non-revenue water as a whole. It is the basis of the NRW assessment matrix and a far more stable target for a regulator than a percentage, which rises in drought years and falls when consumption grows.