Hot water suits are used in cold water commercial surface-supplied diving.[13] A hose in the diver's umbilical line, which links the diver to the surface support, carries the hot water from a heater at the surface down to the suit. The diver controls the flow rate of the water from a valve near his waist, allowing him to vary the warmth of the suit in response to changes in environmental conditions and workload. Tubes inside the suit distribute the water to the limbs, chest, and back.