Epanet
GHydraulics v.2.0.7
GHydraulics is a Quantum GIS plugin that allows to export water supply networks for analysis in EPANET.
Pipe2CAD v.2.05
Pipe2CAD is an AutoCAD add-on freeware that can be used efficiently to complete the design work of pipe networks, such as water supply, sanitary sewer, and storm drainage networks.