The influence of the inclusion of a reaction field on molecular dynamics simulations of liquid water (ST2 model) has been evaluated, both for a momentary and a delayed reaction field. The influence on radial distribution function and energy is not large, but the spatial dipolar correlation is changed considerably. Total dipole moment fluctuations are much enhanced by the reaction field. If the delay of the reaction field is not taken into account, the reaction field effects are overestimated.Dynamic properties are sensitive to the reaction field: the diffusion constant almost doubles and rotational correlation times decrease.Computer simulations were carried out over a total time of 55 ps with a cut-off radius of 0.578 nm and a time of 0.002 ps. The small cut-off and large time step do not influence the accuracy of statistical averages generated by the dynamics run.