In the title hydrated symetrically substituted 1,3-bis(4-methyl-benzyl) benzimidazolium salt, C23H23N2+center dot Br-center dot H2O, the dihedral angles between the benzimidazole ring system (r.m.s. deviation = 0.003 angstrom) and the pendant benzene rings are 73.18 (16) and 77.52 (16)degrees. Both benzene rings lie to the same side of the benzimidazole ring system, giving the cation an overall U-shape. In the crystal, the cation is linked to the water molecule by a short C-H center dot center dot center dot O hydrogen bond and the water molecule forms O-H center dot center dot center dot Br hydrogen bonds. Together, these interactions lead to  chains. The packing is consolidated by C-H center dot center dot center dot Br hydrogen bonds and aromatic pi-pi stacking interactions [centroid-centroid distances = 3.5401 (17) and 3.8815 (18) angstrom], generating a three-dimensional network.