IN THE CRYSTAL STRUCTURE OF THE TITLE COMPOUND [SYSTEMATIC NAME: 1-ethyl-6-fluoro-4-oxo-7-(piperazin-4-ium-1-yl)-1,4-dihydro-quinoline-3-carboxyl-ate sesquihydrate], C(16)H(18)FN(3)O(3)·1.42H(2)O, N-H⋯O and O-H⋯O hydrogen bonds assemble the mol-ecules in a two-dimensional layered corrugated sheet structure parallel to the b axis. The water mol-ecules are disordered [occupancies 0.741 (11) and 0.259 (11)].