Many people believe the water in a hookah filters out the harmful parts of the smoke. It doesn't. The water cools the smoke, which makes it feel smoother, but nicotine, tar, heavy metals and carbon monoxide still reach your lungs.
A session also lasts much longer than a cigarette. According to the World Health Organization, an hour of hookah smoking can mean inhaling many times more smoke than from a single cigarette. The burning coals add carbon monoxide: headache, dizziness or nausea during or after a session are warning signs, so get fresh air straight away.
Sharing a hose can spread infections, which is why every guest should get a fresh mouthpiece. Hookah is for adults only. If you smoke, do it rarely and in well-ventilated places, and never during pregnancy.