In this work the structures of the neutral and zwitterionic forms of norfloxacin, one of the most used FQs, have been evaluated alone, in the presence of one and two water molecules and with each within a reaction field.  The systems have been optimized at the B3LYP/6-31+G* level of density functional theory (DFT), and with the polarizable continuum model (PCM) to examine the differences wrought by hydrogen bonding and by a complete solvent sphere.