Can someone help me find the right water level for this piece please :)

I just have a simple bong and fill it so when I take a hit I don't get water in my mouth.

 

Fill to several millimeters above the percolator on the bottom (the thing with the blue tips)
give it a try and add water until you get a nice steady bubbling on a steady draw
Ok to fill it with water and experiment without material in it
The trolls will be along soon