Previously reported as well as unpublished experimental data for the viscosity of dilute water vapor in the temperature range from (297 to 528) K, which were obtained using an oscillating-disk viscometer, have been re-evaluated and extrapolated to the limit of zero density. The relative combined expanded (k = 2) uncertainty of the re-evaluated data is 0.2 % at room temperature (297 K to 302 K), 0.4 % at higher temperatures up to 450 K, and 1.0 % at temperatures above 450 K. The classical kinetic theory of molecular gases has been applied to compute the viscosity in the limit of zero density for temperatures between (250 and 2500) K using a highly accurate ab initio potential for the H2O molecule pair. In the temperature range from (311 to 438) K, the experimental zero-density data differ by only about +0.1 % from the calculated values. A new correlation for the zero-density limit, based on both the experimental data and the theoretically calculated values, is proposed. The relative combined expanded (k = 2) uncertainty of the correlation is estimated to be 0.4 % between (300 and 500) K, increasing to 0.8 % at 250 K and 2.0 % at 2500 K. The new correlation represents a significant improvement over the current IAPWS zero-density correlation.