Abstract A fit of 450 rotational levels of the 3 vibrational states (020), (100), and (001) of H216O has been performed using 57 effective constants. The Fermi-type interaction between (020) and (100) and the Coriolis type interaction between (100) and (001) as well as between (020) and (001) are taken into account. The part of the Hamiltonian which is diagonal in the vibrational quantum numbers is a Watson-type Hamiltonian. Most of the perturbed levels are well reproduced and the general agreement between experimental and calculated levels is satisfactory with 70% of the calculated ones falling within 15 × 10−3 cm−1 of the observed ones.