Growing global demand for clean water requires the development of materials to address the challenge of water scarcity. Among other materials, carbon nanotubes (CNTs) have attracted much attention in this connection and to optimize them in such applications, information on the molecular level regarding the mechanism of the interactions between CNT walls and water molecules are essential. It is well known that these interactions are not fully understood. Theoretical studies showed that the diffusion of water molecules is size dependent, nevertheless, experimental evidence is still lacking. The complexity arises due to several factors: hydrophobic interaction between water molecules and carbon atoms and the expected change of the water hydrogen bond network upon confinement. Recently, we reported the first 2D NMR diffusion-relaxation experiment on water-CNT systems. In this project, we aim to expand such NMR measurements and to include Atomic Force Microscopy and determine the CNT sizes for optimum water diffusion.