This paper discusses some results of research into reliability engineering for urban sewerage networks, and the possibility of parameter estimation for particular reliability functions so as to establish a database which will enable operational control of the network and its renovation programme. A description and classification of the network failures is proposed for the sewers and the mechanism of their effects upon the soil-water environment will be presented. Very serious consequences am indicated for parametric failures of the networks operated without any program of regular technical state supervision, in the first place without network integrity inspection. The paper aims to underpin the theoretical background for optimal coordination of the renovation process, based upon typical technologies applied nowadays.