The title compound, C(25)H(30)N(4)(2+)center dot 2Br(-)center dot H(2)O, was synthesized from 1,1'-propylenedibenzimidazole and (E)-1-bromobut-2-ene in dimethylformamide solution. The two benzimidazole ring systems are essentially planar, with maximum deviations of 0.011 (4) and 0.023 (3) angstrom. The dihedral angle between these two ring systems is 25.87 (15)degrees. The crystal structure is stabilized by intermolecular O-H center dot center dot center dot Br and C-H center dot center dot center dot Br hydrogen-bonding interactions. Atmospheric water was incorporated into the crystal structure.