Transparent materials such as glass or liquid are quite tricky to reproduce correctly in a real time engine. It is often necessary to cheat to get as close as possible to a pure and slow ray traced rendering.
Sample Project

Fake Glass Material
Liquid Material

Setting up the material

Step 1

Change the Blending Mode: In material panel set “Alpha Blended” in Alpha mode.
You can choose “linear” and reduce the Alpha.

Step 2

Add an environment map and enable environment mapping in material

Step 3

Change the backface cull mode and set to “Double sided” and also add a little bit of rim lighting.

Material Setup
It’s possible to make glass without texture :
Bottle Scene Graph
Liquid Scene Graph

Transparent materials and shadows

Transparent objects will not cast shadows, no matter how blending is done, so you will have to cheat a little.

To avoid this constraint, simply duplicate the transparent object and apply an opaque material on it. And in the options of this material activate “Render Shadows Only”.

The shadow will be cast by this object which is no longer visible.

In reality, a transparent object will not project shadows like an opaque object, but with real-time rendering, it is necessary to make some concessions.

Cast shadows