Water pipes: why ‘lifetime’ is not an adequate concept on which to base pipe renewal strategies

Stakeholders involved in the renewal of drinking water pipes almost always use mean ‘lifetime’ values, which are set by an expert based on material type. A common approach to estimating replacement requirements is to assume that all pipes of the same class of material are renewed when they reach an age equal to their average ‘lifetime’. However, experience shows that for the same type of pipes, very different average ‘lifetime’ values are used, leading to inaccurate estimations of renewal requirements. Furthermore, the notion of ‘lifetime’ can lead to confusion between ‘financial requirements’ and ‘practical rehab requirements’. This study highlights the advantage of considering that pipes of the same class of material can have different lifetimes, the values of which can then be represented in a statistical ‘survival curve’. Replacement needs generated through this curve are then smoothed, allowing realistic annual renewal budgets to be calculated. Given the risk of incorrect evaluation that the term ‘lifetime’ may entail, the term should be avoided when discussing pipe renewal. It would appear preferable to use the term ‘service life’, which clearly expresses the choice to be made by decision makers between repair and renewal.