Mark Engelhardt

Determining maintenance requirements of a water distribution network using whole life costing

A whole life costing (WLC) methodology has been developed for determining long term maintenance expenditure requirements for water distribution networks. The methodology utilises an accounting scheme that ties the costs incurred by the operator and other stakeholders to the attributes or performance that drive the costs. It has specifically been derived with the requirements placed by the regulatory regime on the water companies that operate in England and Wales in mind. Expenditure constraints are implied by the regulator through price caps that companies can charge their customers. Appropriate levels of expenditures included as part of the price cap determinations are required by the regulator to be economically robust and tied to the service received by the customers. Therefore, maintenance decisions must reflect more immediate concerns of meeting performance requirements, but must ensure that such levels are sustainable in the long term. The WLC methodology achieves this through an integrated platform that links costs identified within a structured accounting scheme with their performance based drivers commonly modelled based on historical data. Thus, a robust and fully auditable methodology is provided that can address the requirements of all stakeholders. This methodology is the basis for software (WiLCO) that provides decision support in determining appropriate pipe rehabilitation and operational strategy and thus expenditure levels over extended time horizons.

Quantification of Mains Failure Behavior in a Whole Life Costing Approach to Distribution System Management

A whole life costing (WLC) approach to distribution network management should aim to achieve the lowest network provision and operating cost when all costs are considered to achieve standards enforced by regulation. Cognisance is to be taken of all relevant costs (direct and indirect, private and societal) in order to balance the needs of the service supplier, the customer, society and the environment in a sustainable manner. If this is achieved a WLC framework should enable least cost decisions to reflect the level of risk that a company is willing to tolerate. This approach necessitates estimation of future network performance including the risk of pipe failure. This paper presents the WLC framework which has been developed and a rationale of the style of analysis required to derive factors to describe the risk of failure based on the configuration, quality and extent of available data. From an analysis of homogeneous pipe groups within a large water company pipe asset database covering tens of thousands of kilometres of pipes relationships of failure rate against pipe material, diameter, density of connection and age are presented. Application of these relationships in the derivation of risk factors for use in the WLC approach is discussed. An outline of how costs associated with pipe failure can be incorporated in the WLC approach is given.