This paper reports the results of the chemical composition modeling for an atmospheric pressure DC air discharge with water cathode. The modeling was based on the combined solution of Boltzmann equation for electrons, equations of vibrational kinetics for ground states of N-2, O-2, H2O and NO molecules, equations of chemical kinetics and plasma conductivity equation. Calculations were carried out using experimental values of E/N and gas temperatures for the discharge currents range of 20-50 mA. The effect of H2O concentration on the plasma composition was studied. The main particles of plasma were shown to be O-2(a(1)Delta, b(1)I ) pound, O(P-3), NO, NO2, HNO3, H2O2 and OH. Effective vibrational temperatures of molecules were higher than gas temperature and they did not depend on the discharge current. Distribution functions on vibrational levels for N-2, O-2, H2O and NO ground states were non-equilibrium ones.