Operator terms · Water
What is a fire hydrant?
A fire hydrant is a valved connection to a water main that gives firefighters a high-flow water supply. Operators also use hydrants to flush mains and test flow. Because a hydrant opens the main to the outside, its use and condition affect water quality and pressure.
Last reviewed 2026-08-03
What it is for
The main purpose is fire flow, a large volume of water on demand. Operators also open hydrants to flush sediment out of mains and to measure available flow and pressure in the distribution system.
Why careful operation matters
Opening a hydrant too fast can cause a pressure surge, or water hammer, and stir up sediment. Operators open and close hydrants slowly and check that they drain properly so they do not freeze or hold stale water.
Common questions
- What is a fire hydrant connected to?
- A water main in the distribution system.
- Do operators use hydrants for more than fires?
- Yes; for flushing mains and testing flow and pressure.
- Why open a hydrant slowly?
- To avoid a pressure surge, water hammer, and stirred-up sediment.