Catalyst activity during the carbon nanotubes (CNTs) growth by chemical vapor deposition (CVD) is enhanced when water, a weak oxidizer, is introduced together with the carbon source. The height as well as the CNTs density can be controlled by fine-tuning the water content. The characterization of the mechanical properties of CNTs produced by the water assisted CVD process clearly indicates that high quality materials are produced. CNTs with diameter smaller than 12 nm exhibit Young's modulus higher than 400 GPa. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim