Field assessment of performance-based leakage reduction contracting indexed on minimum night flow in a Moroccan network

Night flow falls from 76.2 to 35.7 L/s over two contract cycles and rebounds at a measured 17.1 L/s per year between them. Performance-based contracts are increasingly promoted for water loss reduction in middle-income countries, yet empirical evaluations of contracts remunerated on the minimum night flow are largely absent from the peer-reviewed literature. This study evaluated a two-year performance-based leak detection and repair contract covering a 212 km network with 15,500 service connections in Ain Aouda, Morocco, using 39 validated measurement nights across 14 campaigns, a georeferenced register of 1,229 repaired leaks, matched-site pressure records, and fully observed cost records. The contractor reduced the minimum night flow from 76.2 to 45.7 L/s on schedule; leakage then rebounded to 55.6 L/s within six months, yielding a natural rate of rise of unreported leakage of 17.1 L/s per year, before a second campaign reduced night flow to 35.7 L/s (a 53% reduction). Night pressures at matched sites were stable or lower during the rebound, excluding a pressure artifact and making the estimate conservative. With a measured night-day factor of 19.0 hours, the economic intervention interval from observed costs is 3 to 8 months as a central estimate, against 19 practiced, and the incremental cost of active leakage control lies below the utility's full cost of water. Design recommendations are proposed for night-flow-indexed contracts.