A detailed analysis on the geometrical and electronic properties of confined water nanostructures in pristine and functionalized (7,0) and (10,0) carbon nanotubes (CNT) is presented. Confined water molecules within these CNTs form similar 'water-chain', 'water-cluster' and 'water-tube' like nanostructures. From the analysis of electronic properties it is clearly evident that the formation of these nanostructures is determined by the interplay between water lone-pair-CNT pi orbital interaction and hydrogen bonding between water molecules. (c) 2012 Elsevier B.V. All rights reserved.