The density of water calculated through molecular dynamic simulations using different water models and rigid/flexible carbon nanotubes is studied. A previous equation, determined in an earlier work in order to correlate density and nanotube diameter, is tested against these new data. It is demonstrated that this equation provides a reasonable approximation for all the configurations investigated. It is also confirmed that the use of flexible nanotube models does not bring any significant improvement and the average carbon dislocation is small compared to the size of the water molecules. Comparison between SPC/E and TIP3P models, furthermore, shows that the first model leads to polygonal water structures, which are not evident in the other case. (C) 2008 Elsevier Ltd. All rights reserved.