A fire hydrant is an active fire protection measure, and a source of water provided in most urban, suburban and rural areas with municipal water service to enable firefighters to tap into the municipal water supply to assist in extinguishing a fire.
In areas subject to freezing temperatures, only a portion of the hydrant is above ground. This design is known as a “dry barrel” hydrant, in that the barrel, or vertical body of the hydrant, is normally dry. A drain valve underground opens when the water valve is completely closed; this allows all water to drain from the hydrant body to prevent the hydrant from freezing.
In warm areas, hydrants are used with one or more valves in the above-ground portion. Unlike cold-weather hydrants, it is possible to turn the water supply on and off to each port. This style is known as a “wet barrel” hydrant. Both wet- and dry-barrel hydrants typically have multiple outlets.