Active leakage control
There are very few distribution systems that do not experience unreported leaks, to a greater or lesser extent. The leaking water flows into drains, permeable ground or underlying fractured rocks, without causing any immediate problem. Active Leakage Control is the activity of identifying the presence of such events, and going out to locate them (intervention), so as to control their average run time.
The economic frequency of intervention depends on the value of the lost water ($/m3), the cost of intervention ($/km of mains or $/service connection), and the average 'rate of rise' of unreported leakage from one year to the next. Rate of Rise varies widely for different systems and sub-systems, but it can be assessed from annual water balances, night flow measurements, or numbers and types of leaks found in successive interventions. The economic frequency of intervention, and an appropriate annual budget for commencing active leakage control, can then be quickly calculated (Ref 3).
Ref 3: Lambert A and Lalonde A (2005): Using practical predictions of Economic Intervention Frequency to calculate Short-Run Economic Leakage Level, with or without Pressure Management. Proceedings of IWA Special Conferences 'Leakage 2005' , Halifax, Nova Scotia, Canada, Sept 2005