Towards pro-active rehabilitation planning of water supply systems

Making decisions on the renewal of a water distribution system is essentially a balancing act between system performance and costs. In water distribution systems three types of failure are observed, structural, hydraulic and water quality. Frequencies of these failures together with failure consequences define failure risk. Risk can thus be mitigated by a reduction of failure frequency, i.e., renewal, and/or limiting failure consequences. Life-cycle cost comprises risk (or the expected consequences of failure), cost of renewal and reduction of failure consequences. Sound decision should minimise this life-cycle cost, but to achieve this goal one must be able to quantify risks. In this paper the critical elements of a holistic view of water supply systems are identified and these are discussed in relation to the current state-of-practice and future research directions towards the pro-active planning of their renewal. While various models are available to analyse water main breaks, commensurate efforts need to be dedicated towards analyses of water quality and hydraulic failures.