A Comprehensive Guide to Fire Hydrants

When taking a stroll through your neighborhood, you’re bound to see one sooner or later. We’re talking, of course, about fire hydrants. Your dog loves them, but you’re more curious about them than anything. How do fire hydrants work?

Fire hydrants provide an instant water supply to firefighters, as underground, the hydrant is connected to a series of pipes. These pipes lead to the water supply main. To use the fire hydrant, the firefighters will release a hydrant nozzle, attach their hose to the nozzle, and then twist a valve to get pressurized water.

Even outside of firefighting, fire hydrants are fascinating things. In this guide, we’ll tell you everything you need to know about fire hydrants, including what they are, the types of hydrants, how they work, what their colors mean, and whether they count as public property. 

Types of Fire Hydrants 

Okay, so what exactly is a fire hydrant, anyway?

We’ll talk in the next section about the underground components of a fire hydrant, but for now, this is all about the hydrant itself. A fire hydrant is typically made of ductile iron or cast iron for durability.

The hydrant will feature bronze or waterworks brass for the nozzles, drain valve area, and the main valve.

Used all over the world, fire hydrants are installed near a water main (usually within 24 inches). They’re almost always by a pavement edge or a curb due to the water main location.

The average height of a fire hydrant is three feet.

Having existed since the 19th century as an above-ground feature, fire hydrants are shaped like pillars.

They tend to have rounded, triangular tops with protruding valves on the sides. Here are the parts of a fire hydrant:

  • Valves: The valves are one of the most distinct components of a fire hydrant, as mentioned in the paragraph above. These valves are often closed by default but can be opened by a firefighter when needed. 
  • Stem nut: To use any of the valves included with a fire hydrant, the stem nut comes into play. This pentagon-shaped nut allows for access to the fire hydrant’s operating stem, which opens the valves. 
  • Outlets: All fire hydrants have outlets, but how many and their sizes vary based on the type of hydrant. The outlets may include a pumper outlet for the firefighters to attach to their pumper trucks. 
  • Flange: The flange is an attachment point for the fire hydrant and is located at the hydrant’s base. 
  • Bonnet: The fire hydrant’s cap is known as its bonnet. Within the bonnet is the operating stem nut. The bonnet is for more than just looks, by the way, but also for preventing water penetration and other damage from shortening the lifespan of the fire hydrant. 

Even though all fire hydrants have these parts, there are still two distinct types of hydrants. The first is a wet barrel fire hydrant. You’ll see these more in Florida and southern California than the rest of the United States due to the warm weather there. 

Wet barrel fire hydrants always have water in them without the need to set the valves to an open position. The operating stems are nearer to outlets, and there tends to be more of these stems per fire hydrant.

The other and much more prevalent type of hydrant is the dry barrel hydrant. The name tells you that these fire hydrants start out empty so the water doesn’t freeze when it’s not in use. 

How Does a Fire Hydrant Work?

Okay, so those are the basics on fire hydrants, but as we said, the hydrant is one part of a larger system. You only see the fire hydrant, so it’s easy to forget all of what’s underground, but there’s plenty.

The fire hydrant connects to a travel drain basin, which holds the water runoff as it accumulates.

The basin is a long, vertical-running tube that connects to the thrust block. This small section of pipe regulates the internal water pressure so the fittings and pipes don’t separate.

The thrust bock also provides stability to the surrounding soil.

The thrust block is usually reinforced with concrete supports on either side. It connects next to a joint-restraining gland, a type of restrained joint system that also prevents joint separation from occurring.

The pipework, which was vertical to this point, now begins running horizontally at the gate valve. The gate valve can connect to a firefighter’s supply line so they can separate the hoseline.

This comes in handy if the fire hydrant valve happens to get stuck in an on position, which can occur at times. 

The gate valve is connected to two parts. Atop the gate valve and protruding vertically up to the finished-grade concrete or asphalt is the valve box lid. This is the cover for the valve box, the second of the two components. The valve box encloses the irrigation system’s parts.

Finally, the gate valve connects to the local supply main, which is the neighborhood’s source of water. 

The valves of a dry barrel fire hydrant can be set in one of two positions: closed or open.

When closed, the valve prevents the water from moving. The fire hydrant’s drain holes also open when the valves are closed so the hydrant barrel remains empty and its contents don’t freeze.

When set to open, a dry barrel fire hydrant’s drain holes are plugged due to the bottom valve. This allows water to fill up the hydrant so the firefighting team can use it. 

To access a fire hydrant’s valve covers, the firefighters will use what’s known as a hydrant wrench. With the covers off, the fire department connects their hoses to the fire hydrant valves.

The water then leaves the fire hydrant, passing through the firefighter’s hoses, and undergoes pressurization to spray at a strong enough rate to contain a fire. 

What Do Fire Hydrant Colors Represent?

If there’s one color associated with firefighting, it’s red. That’s why you sometimes hear of bright, ruby red hues being described as fire engine red.

Fire hydrants are usually red as well, or are they? Well, not always.

The other color of fire hydrants is yellow. The reason fire hydrants are painted either red or yellow is that these are bright, eye-catching colors.

Firefighters need to be able to spot a fire hydrant so they can quickly connect to it and get its water. It’s hard to miss a yellow or red hydrant.

Fire hydrants aren’t always one color, by the way. Some have a separate hue for the bonnets. This isn’t for appeal, but rather, the color of the bonnet quickly tells a firefighter how much water the fire hydrant can hold.

It may vary from place to place, but if the fire hydrant has a red bonnet, then it’s a Class C that contains 500 gallons per minute or GPM of water or less.

An orange bonnet is a Class B with at least 1,000 GPM of water. If you see a green bonnet on a fire hydrant, that’s a Class A that contains 1,500 GPM of water.

The most plentiful fire hydrants are those with light blue bonnets. These are Class AA and within them is more than 1,500 GPM of water.

What Is the Max Flow Rate and PSI of Fire Hydrants?

The max flow rate as represented in GPM and the top pressure per square inch or PSI of a fire hydrant depends on its hoseline size. Hoselines can be medium-diameter or large-diameter. 

The medium-diameter hoseline is about two and a half inches on average, and two hoselines will be used at a time. This setup provides 26 gallons of water for every 100 feet. 

By increasing the medium-diameter hoseline to three-inch hoses (again, two of them) you may have a more effective setup.

Already, for every 100 feet, you get more water at 36 gallons. The water pressure is less though due to friction loss.

A large-diameter hoseline is regarded as the best option, as the hose allows for more water to travel and cuts down even further on friction loss.

Five-inch hoseline is common, and for every 100 feet, the hose provides 100 gallons of water. That’s 64 more gallons than what you get with the dual three-inch medium-diameter supply lines and 74 more gallons than with dual two-and-a-half-inch medium-diameter supply lines.

Are Fire Hydrants Considered Public or Private Property?

Who owns a fire hydrant? Is it the fire department? The town or city? Some private owner?

That depends on the location of the hydrant.

Anytime a fire hydrant is on public property, it’s considered publicly owned by the city or town in which it’s located. 

It’s up to the city or town to inspect the condition of the fire hydrant (or hire a professional to do so), test the hydrant, and maintain it so it’s useful to firefighters for as long as possible. 

However, not every fire hydrant you see is necessarily public property.

If a hydrant is on a private lot such as someone’s home, then it’s considered private property. The International Fire Code or IFC has rules on how much water a private fire hydrant can contain. 

Some private fire hydrants have the same bonnet colors per water flow rate as public hydrants. 

The onus on inspecting and maintaining the fire hydrant is that of the property owner since it’s their hydrant.

Every year, they should thoroughly inspect the fire hydrant, especially the areas of exposed valves and piping. They also have to inspect the surrounding underground piping. 

The testing component includes trying the underground pipes at least once every five years if not more often.

The fire hydrant owner must also test for the drainage capabilities of wall or dry barrel fire hydrants as well as the flow of the hydrant once a year.

Maintenance encompasses clearing ice and snow from the fire hydrant as these accumulate. The hydrant owner has to prevent mechanical and other damage to the fire hydrant as well. If any threads, plugs, caps, and/or stems are dried out, the hydrant owner must lubricate these. 

It’s a lot of responsibility owning a fire hydrant, but some people do indeed decide it’s within their best interest to have their own hydrant. You’re much more likely to come across public fire hydrants though. 


A fire hydrant might look like a simple apparatus, but it’s connected to a series of underground pipes, including your city or town’s main water supply line. The hydrant can fill up with water to provide a pressurized water stream to the fire department so they can quickly put out fires.  

Now that you’re much more well-versed in fire hydrants, you can enjoy a greater appreciation for them and their life-saving capabilities!

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