The Nanotechnology Research Institute of the National Institute of Advanced Industrial Science and Technology and Graduate School of Science in Tokyo Metropolitan University have performed a detailed analysis of the structure of water in a single-walled carbon nanotube (SWCNT) by means of X-ray structural analysis conducted at the Photon Factory of the High Energy Accelerator Research Organization (KEK), an inter-university research institute corporation. The detailed structural analysis found that water within SWCNT forms tubular ice, called ice nanotube (Ice-NT), at lower temperatures. It was found that there was a tendency for the melting point of Ice-NT to vary greatly depending on the diameter of the SWCNT, with the melting point becoming higher as the diameter of the SWCNT becomes narrower, contrary to existing empirical rules. In particular, water in SWCNT with a diameter of 1.17 nm crystallizes at 300 K or lower. In other words, it was proved that Ice-NT could be formed at room temperature. Moreover, it was discovered that, at approximately 45 °C , water within SWCNT would vaporize and be ejected, leading to the possibility of a number of applications, including nano-size inkjet printing.