High Quality Content by WIKIPEDIA articles! A fire hydrant (also known colloquially as a fire plug in the United States or as a johnny pump in New York City), 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. Buildings near a hydrant may qualify for an insurance discount since firefighters should be able to more rapidly extinguish a fire on the insured property.