In this work we analyze the effect of a single water molecule on the glyoxal+OH reaction, using quantum chemistry and computational kinetics calculations in a pseudo-second order mechanism, taking into account average atmospheric water concentrations and temperatures. We show that, although the formation of a hydrogen bonded glyoxal–water complex decreases the energy of the transition state barrier, the concentration of this complex is much too small to be relevant, and consequently a reaction rate enhancement by a single-water-molecule catalysis does not occur under tropospheric conditions.