In the title compound, C(12)H(14)N(4)·6H(2)O, the two pyrimidine rings make a dihedral angle of 5.285 (6)°. Inter-molecular O-H⋯O hydrogen bonds link the six water mol-ecules, generating edge-fused four-, five- or six-membered ring motifs and forming two-dimensional sheets. The sheets are stabilized by the formation of O-H⋯N hydrogen bonds between the water mol-ecules and the bipyrimidine mol-ecules, resulting in a three-dimensional network.