Material rendering problem

When I created my first water shader in UE4 it had this problem, now I have a bit better one but I don’t have any idea of what’s going on and why is it rendering wrong.

You can see on screenshots what I mean.

First is top side of material and second side of material.

Generaly I can see second side of material. Is there any fix for this or any workarround?

Link to screenshots: