Will state of water change in certain condition? Imagine I have an iron tank with a $20~\mathrm{pm}$ hole on it. Then I completely fill it with water and use a pump to get the water out of that hole. What will come out, water or gas?
 A: Your hole is too small to let even a single molecule through, but let's increase the hole to a size where molecules can come through one at a time. I'm sure this is what you had in mind. What then would be the result?
And the answer is that would have created a molecular beam. That is you would have a beam of isolated water molecules travelling away from the hole. The kinetic energy of the molecules would be about the thermal energy of $\tfrac32kT$. I make this a velocity of about 450 m/s.
A: Pressure alone does not break chemical bonds. Expose liquid water suddenly to a vacuum and it will vaporize as a molecule; it will not dissociate into atoms. This is true regardless of the initial pressure of the water.
The hole that you have made is too small for water molecules. It is even too small for a hydrogen atom, which is the smallest atom possible (with a radius of about 50-60 pm).
The hole size that you propose is more akin to the sizes of interstitial sites in solid lattices. For examples of the lattice structures of iron, see the links below.
https://en.wikipedia.org/wiki/Allotropes_of_iron
https://www.tf.uni-kiel.de/matwis/amat/iss/kap_4/backbone/r4_2_2.html
At this point, you should recognize that we cannot make a contiguous "hole" that is 20pm in radius or diameter through an iron wall. Indeed, this because of the way that atoms pack in solids, we cannot make such a hole through any solid wall that is thicker than two atoms stacked on in layers. The "holes" through the one layer of atoms are blocked by the atoms that cover in the next layer.
In essence, you have a solid tank. Nothing will transport through the wall.
