Be careful!
Hookah diving involves breathing compressed gas, and therefore you should use a dive table or computer. If you are diving to a max depth of around 15', then you literally have hours of bottom time without having to do decompression STOPS, but all compressed gas diving involves decompression. In the cases where a deco stop is not needed, you are still required to ascend at a slow rate: this is an extremely important aspect of all compressed gas diving. Whether you're on the end of a hose or breathing from tanks, and whether you're breathing air, nitrox, or other mixes is really irrelevant as far as decompression is concerned, it's just the logistics that are different.
If you are breathing compressed gas (which you are when on a hookah) you must never hold your breath, EVER. 4 metres of seawater is more than enough to cause an embolism upon ascent. The gas you're breathing is compressed; it doesn't have anything to do with what the gases are.
Anyone who wants to use a hookah should take a scuba course first....there are things you must know before breathing compressed gases.
Cheers,
Erik Y.