Water not having selection box problem

I am making a mod that adds forged iron, and I want it to have a similar functionality to the bottle, as in when you right click water it changes the item in your hand. The problem is I can't seem to get the water block's position, as it doesn't have a selection box. I also want to make it so you can right click a cauldron that has water in it to cool the forged iron, but it isn't necessary.