The title compound {systematic name: 7-[(1S,6S)-8-aza-2-azonia-bicyclo-[4.3.0]non-8-yl]-1-cyclo-propyl-6-fluoro-8-meth-oxy-4-oxo-1,4-dihydro-quinoline-3-carb-oxy-lic acid chloride monohydrate}, C(21)H(25)FN(3)O(4) (+)·Cl(-)·H(2)O, crystallizes with two moxi-floxa-cinium cations, two chloride ions and two uncoordinated water mol-ecules in the unit cell. The crystal structure has a pseudo-inversion center except for the chloride ions. In both moxi-floxa-cinium cations, the quinoline rings are approximately planar, the maximum atomic deviations being 0.107 (3) and 0.118 (3) Å. The piperidine rings adopt a chair conformation while the pyrrolidine rings display a half-chair conformation. In the crystal, the carboxyl groups, the protonated piperidyl groups, the uncoordinated water mol-ecule and chloride anions participate in O-H⋯O, O-H⋯Cl and N-H⋯Cl hydrogen bonding; weak inter-molecular C-H⋯O and C-H⋯Cl hydrogen bonding is also present in the crystal structure.