Molecular dynamics simulations are performed to understand the characteristics of the one-dimensional Brownian motion of water columns inside carbon nanotubes (CNTs) at room temperature. It is found that the probability of 2–10-nm-long water columns sliding a distance larger than the energy barrier period inside 2–5-nm-diameter CNTs is greater than 50 %. Moreover, a conservative estimation gives that the thermal fluctuation-induced driving force exceeds the upper bound of the sliding energy barrier for a water column shorter than 117 nm. These findings imply that although water molecules form layered structures near the CNT inner walls, there is no critical interfacial shear stress to conquer, and water could slip inside CNTs under any given pressure drop due to the thermal activation at room temperature.