How to place a block on the same side as the player?

As the name suggests, I'm not sure on how I can place a block on a certain side of another block when right-clicked.

I'm currently making an item that places water whenever you right-click on a block, but with my current procedure it replaces the block I'm looking at instead of on the side of the block.

Everywhere I have looked for such information has been unhelpful and I'm not sure if this is possible, but any help would be greatly appreciated!