Many different patents were used to create various fire hydrant types. Wooden outer encasements were used before the more familiar cast iron fire hydrant cover commonly seen today. The American Water Works Association (AWWA) regulates the design of fire hydrants in the United States to meet fire district standards.
Dry barrel and wet barrel are the two kinds of fire hydrants. The wet barrel fire hydrant holds a constant water supply, while the dry barrel fire hydrant needs to have a valve release to let water in. The main benefit of a dry barrel fire hydrant is that its design avoids a frozen water supply in very cold climates. Some wet barrelled fire hydrants may be made of bronze rather than iron, or they may have an inside finish that avoids rusting.
The barrel of a fire hydrant may also be known as a “standpipe.” Some fire hydrants are rounded in style, while others have more angular lines. The outlets on a fire hydrant are usually made of bronze, but the caps may be made from other types of metal.