New measurements have been made for the viscosity (77) of light and heavy water between the temperatures of 255.65 K and 298.15 K at pressures up to approximately 375 MPa with a falling-body viscometer. A revised correlation function is used to represent the results as a function of temperature and molar volume (V) with a standard deviation of +/-0.2% for both H2O and D2O. The overall uncertainty is estimated at +/-1%. Comparison of the two sets of data shows that they are consistent with the correlation eta(D2O,T,V) = 1.0544eta(H2O,T - 6.498 K,V) where 1.0544 is the square root of ratio the molar masses and 6.498 K is the thermal offset proposed by Robinson and co-workers.