Research had prior to CARE-S been carried out in a major international (IWA) project to define appropriate performance indicators (PI) for wastewater systems.

The objective of this work package, in straight connection with the previous project CARE-W, was to select and define those indicators that are relevant for the analysis of short-term as well as long-term wastewater network rehabilitation needs.

The performance indicators are independent of the system. They can be used in two different ways to define rehabilitation policies: (i) to support immediate decisions about the short-term rehabilitation needs, and (ii) to understand the current system behaviour and compare alternative design solutions. The latter takes into account several aspects, namely technical, socio-economic and financial, allowing for long term pro-active planning. The former type of performance analysis is mainly based on sound records, such as damage rate or maintenance costs, or on data obtained from systematic or ad-hoc field surveys. The latter type require the use of hydraulic and water quality simulation tools or the data from monitoring schemes, in order to infer the system's behaviour if a given rehabilitation option were implemented. The approach that was adopted was system independent and was common to all the indicators. These characteristics allowed us to reach a common consensus on how rehabilitation criteria may be expressed. On the other hand, it had the capability to be customised integrating specific aspects related to local design and operating practices.

From the technical point of view, performance can be assessed based on hydraulic, environmental and structural-related aspects. However, in modern societies, performance of a sewer system can not be assessed exclusively based on technical aspects. Economic and social points of view are becoming more and more important. It was therefore necessary to take all these aspects into consideration and select for each one of them the relevant indicators. The economic and social aspects were also developed within the scope of these projects (see WP 4) with experts in the field.