The kinetics of forming and breaking water-water hydrogen bonds in neat water, an aqueous solution of ethane, and an aqueous solution of NaCl are studied by molecular dynamics simulations. We compare nonpolarizable and polarizable water models to elucidate the effect of water's polarizability on hydrogen bonds. We find that polarizability strengthens the hydrogen bonds and increases the hydrogen bond relaxation time by a factor of between 50% and 100%. The Gibbs energy of activation for breaking hydrogen bonds is similar to0.2 kcal(.)mol(-1) higher for the polarizable water model. Polarizability also causes the rate of forming and breaking hydrogen bonds to be more dependent on the local environment.