Water pipe network systems are key public utilities which require being robust, protected and preserved. Knowing their weaknesses will help these processes. The theory of vulnerability of water pipe networks can contribute in this context because it is able to map the vulnerable parts of this type of system. The meaning of vulnerability has been defined as being the disproportionateness of the failure consequences in relation to the initial damage and, in particular, its theoretical concepts. The main objectives of this paper are to briefly introduce this theory, to illustrate its application highlighting its potential. The application of the theory is presented using an example of a simple water pipe network. In a real water supply utility, where the vulnerabilities of WPN components are less evident, the identification of the most vulnerable ones may play an important contribution as support decision during WPN design period and for a sustainable infrastructure asset management. Further work is in progress to account for different type of damage and consequences and thus manage risks due to failure scenarios not identified by the classical theories.