Optimization of water distribution is a crucial issue which has been targeted by many modelling tools. Useful models, implemented several decades ago, need to be updated and implemented in more powerful computing environments. This paper presents the distributed and redesigned version of a legacy hydraulic simulation software written in Fortran (IRMA) that has been used for over 30 years by the Société du Canal de Provence in order to design and to maintain water distribution networks. IRMA was developed aiming mainly at the treatment of irrigation networks -by using the Clément demand model and is now used to manage more than 6.000 km of piped networks. The growing complexity and size of networks requested to redesign the code by using modern tools and language (Java) and also to run distributed simulations by using the ProActive Parallel Suite.