Hookah rigs deliver air from a compressor on the surface down to a diver below, just like those old school cartoons. Divers doing serious long term jobs underwater may opt for these regulators, which are specially designed for hookah style diving. Please bear in mind that a regular scuba diving regulator cannot be used for hookah applications! Hookah regulators function with a different set of pressures and have specific regulators for specific conditions.
A Hookah regulator setup is entirely different from a scuba regulator. It consists of a 'second stage' only, which is fed directly from the output of the reserve tank via a Hookah air hose. There are no tank valve and first stage regulator assemblies of the type that are used with scuba cylinders.
Hookah second stage regulators typically employ a 'tilt', or 'pin' valve, which delivers a full airflow to the diver at low-pressure. This type of regulator is specifically designed for use with low-pressure Hookah compressors. Hookah second stage regulators, as are all modern regulators, are of the single hose, 'demand' type. A 'demand' regulator works on a relatively low volume of air since it only has to deliver air as the diver breathes, or 'demands' it.
Scuba second stage regulators typically can't be used for Hookah applications without special modifications. A typical Hookah compressor operates in a low-pressure range which is not enough pressure to drive the spring-loaded downstream valve of a scuba second stage regulator.
A diver who already owns a scuba second stage regulator, but who wishes to use it for Hookah applications, must take the regulator to a competent dive shop and get the regulator converted over for low-pressure use. The conversion can be made by installing a set of low tension springs which will give maximum efficiency when operated at low Hookah pressures. A dive shop will also have the necessary test equipment to make certain the adaptation has been effective.
Please read Introduction to Hookah Diving for more information about things you need to consider with a hookah diving setup.