H-1 nuclear magnetic resonance was used to measure water adsorption isotherms at room temperature in cut single-walled carbon nanotubes (SWNTs) and activated carbon (AC). Although the level of water adsorption inside SWNTs is as high as in any AC, the adsorption isotherm reveals the lack of wetting inside cut-SWNTs. Quantitative analysis and various effects of adsorbed D2O on gas adsorption inside cut-SWNTs indicate that adsorbed water molecules reside mostly near principal adsorption sites associated with tube ends and defects. (c) 2006 Elsevier B.V. All rights reserved.