13.1 INTRODUCTION

Water distribution networks in industrialized countries are aging; many of them have pipes more than 50 years old. Therefore, much rehabilitation or renewal work appears to be necessary in the future to keep this infrastructure in good condition. In addition, regulations concerning water quality have become stricter and impose heavy investment costs on water utilities. So, choices need to be made in order to meet investment needs and water regulation responsibilities while keeping costs within the available budget. Up to now, renewal decisions have been mainly made with regard to the failure rate and in relation to roadworks planning. The present decision process is essentially curative; it seems therefore necessary to propose a proactive methodology for planning the renewal decisions.

13.2 WHAT IS A PLANNING PROCESS FOR RENEWAL?

The planning process for renewal can be divided into four steps:

1. The diagnostic of the network s health, which is based on the network s characteristics, environment, and history. This step gives information on the aging and alteration of the network through physical factors (failures, corrosion, water quality, etc.), as well as about the pipe s close environment.

   The second step takes into account the results of step 1, but also takes into account economic and sociologic factors in order to optimize the renewal date. This optimization is made without constraints. So, on one hand it leads to a classification of the pipes and the identification of the most risky ones; on the other hand it...