Water at different physical states has been attracting great interest for decades for their strong association with the origin of life, the biophysical behaviors of biomacromolecules, and the transportation of matter and energy. The structurally well-defined, monodispersed nano-capsules provide golden opportunities to understand water sciences under confinement. Here we show, a group of porous, hollow polyoxometalates with varied inner ligands have been studied for the distributions of water inside them in solutions via contrast variation small angle neutron scattering (CV-SANS) techniques. Meanwhile, molecular dynamics simulations have been conducted to cross-examine fitting results of SANS data and provide structural details of the formation of such water distribution pattern. Our work suggests that the densities of water in the core of nano-capsules highly rely on the dimensions of hydrophobic confinement space (cores inside nano-capsules) and can approach to dewetting state at critical dimension, ca. 1.1 nm.