The title compound, C(21)H(21)N(5)O(2)·0.5H(2)O, has two fused six-membered rings linked to a benzene ring and to a triazole ring, which is connected to a butanol group. The quinazoline ring forms a dihedral angle of 7.88 (8)° with the benzene ring, while the triazole ring is approximately perpendicular to the benzene ring and to the quinazoline system, making dihedral angles of 84.38 (10) and 76.55 (8)°, respectively. The stereochemical arrangement of the butanol chain, with a C-C-C-C torsion angle of 178.34 (19)°, corresponds to an anti-periplanar conformation. However the position of the -OH group is split into two very close [O-O = 0.810(3) Å] positions of equal occupancy. The crystal structure features O-H⋯N and O-H⋯O hydrogen bonds, building an infinite three-dimensional network. The water molecule is located on a half-filled general position.