H-1 MAS NMR study of water absorbed in open single-wall carbon nanotubes (SWCNTs) of average diameter 1.0 nm, synthesized with a Fe catalyst, was performed. Magic angle spinning significantly increases the spectral resolution and the spectrum shows that there are at least two distinct chemical shift regions for the water proton. From temperature dependent measurements, we assign the two chemical shift ranges to water absorbed inside and outside the nanotube. The spectra as a function of the water content show that the first water molecules that are absorbed by the dry material are absorbed inside the tubes. (c) 2006 Elsevier B.V. All rights reserved.