EPANET on Linux: Download RPMs, DEBs and source code
EPANET's graphical user interface: epanet2w.exe
The Windows version of EPANET can be run on Linux using the Windows emulator software Wine. The following installation steps work on Ubuntu 12.04:
sudo apt-get install wine wget http://www.epa.gov/nrmrl/wswrd/dw/epanet/EN2setup.exe wine EN2setup.exe
EPANET is open source and compiles well on Linux using gcc. Prebuilt binary packages for several distributions are available for those who don't want to compile themselves.
Ubuntu DEB package
Fedora RPM package
openSUSE RPM package
Use the standard ./configure, make, make to build and install.