In the title compound, C(25)H(35)N(2) (+)·Cl(-)·H(2)O, the imidazolidine ring adopts a twisted conformation, with a pseudo-twofold axis passing through the N-C-N carbon and the opposite C-C bond. The N-C-N fragment of the imidazolidine ring shows some degree of both double- and single-bond character due to partial electron delocalization. One of the tert-butyl groups is disordered over two conformations with occupancies of 0.714 (8) and 0.286 (8). In the crystal, O-H⋯Cl and C-H⋯O hydrogen bonds help to establish the packing.