We arc reporting gravimetric measurements of adsorption isotherms and kinetics of water vapor in single-walled carbon nanotubes (SWNTs). Adsorption was facilitated in an open configuration. Adsorption capacities of SWNTs were found to be approximately one-half of those of activated carbon and activated carbon fiber. The water adsorption isotherms of SWNTs followed type V characteristics, which are typical for a surface chemistry mediated adsorption of water. The isotherm models, the Dubinin-Serpinski equation and the Do equation, were fitted to the SWNT isotherms. The information about the SWNT surface chemistry could be extracted from data fitting to these equations and was found to be consistent with the same observed from Raman scattering of the SWNTs. The adsorption and desorption rate constants were calculated for all SWNT samples as a function of relative pressure using the linear-driving force model commonly used for activated carbons. The rate constants for both carbon types were in the general range of 1 x 10(-1) to 3 x 10(-3) s(-1) with values decreasing with increasing vapor pressure; however, the distinction between adsorption on the primary sites versus capillary condensation was not apparent for SWNTs. This work can provide descriptive experimental data (detection limit = 0.1 mu g) to aid molecular simulation studies of water adsorption in microporous and nanoporous carbon adsorbents.