With glass on glass water pipe and slider pipes, your joint where you pull your bowl from becomes the carb! This actually works better as the fresh air with comes through the water to push the smoke up and out into your lungs instead of a slipstream from the side adding in air. This will also humidify the air coming in and makes the hit smoother.
If you ever want a water pipe with a carb in it, the crew at Elev8 Premier can make it for you.