EPANET is a very nice ...
Published by Joaquim Sousa, Superior Institue of Engineering - Coimbra / Portugal
EPANET is a very nice software to start, but you can try WaterNetGen. It is an EPANET based software with some interesting features, like Pressure-Driven-Analysis (to model leakage as I think you want to), pipe design (including new netowrks, existing networks or expansions), and many other. It is free to use and you can download it from: http://www.dec.uc.pt/~WaterNetGen/waternetgen.php?DownLoadData=Nothing