Rim mount faucet on tub

Because of how my bathroom is laid out I need to be able to mount a faucet on the rim of my fiberglass tub. Can this only be done with certain tubs? I read the specs for the Kohler Lakewood model and they say the following:

"Consult national and local codes for minimum air gap requirements if installing a spout on the faucet deck."

What is the air gap they are referring to?


Thank you,

Eric

air gap

The distance between the point where water would spill out of the tub and the end of the spout where the water comes out. It normally should be at least 2" to be safe and legal. If the tub has a flat surface, which is sometimes reinforced underneath, that is where you would mount the faucet.

Thanks HJ.