Rendering water in blocks

Hello there!

I want to make an water bucket to be pleaceble on top of a block.

I have modeled the block in Blockbench and made two versions: "Empty" and "Water Filled". 

For the "Water Filled", I created a "filling" cube that is inside the bucket and for testing, painted it blue with low opacity.

I checked some tutorials and tried to set the block rendering to be "transluscent", but it seems to not affect anything.

I am having issues making the "filling" cube look like the rest of the water of the game - I want it to look somewhat like the cauldron when it is filled with water.

Anyone has any idea of how to get this cube inside the bucket to actually look like water?