How does a water cannon work?

A firefighter battles a wildfire with a high-powered water cannon from atop a fire engine.
Donald Miralle/Getty Images News/Getty Images

Whether you're looking to squelch a roaring apartment fire, stop a prison riot or crack down on a little free speech, there's one important piece of technology you'll want at your disposal: the water cannon. While animals such as the bombardier beetle and various species of cephal­opods have possessed the ability to shoot powerful jets of fluid for millions of years, human technology has only caught up over the last few centuries.

Although recent years have seen the increased use of water cannons as a nonviolent crowd control measure, 18th and 19th century citizens were far more concerned with controlling urban fires. Before the advent of the water cannon, fire brigades depended largely on bucket lines, in which firefighters passed bucket after bucket up to the front of the line to douse the flames. Obviously, this put severe limits on what firefighters could accomplish. Sometimes the only option was to dynamite the burning building in an attempt to suffocate the flame or to tear down adjacent buildings, creating a firebreak to keep the destruction from spreading.


­During the 16th century, firefighting organizations such as the London Fire Brigade began to use simple water cannons. Some of these were essentially hand-held plunger devices -- much like a large syringe or some of the water guns you'd find in a toy store today. Other water cannons implemented a primitive version of what would become the modern standard: a pumping system, water tank and a water cannon or deluge gun. While a few firefighters manually worked the pumps, another aimed the water cannon at the flames. Some of these systems still required manual bucketing to keep the tank filled, but improved hose construction soon cut out all the elbow work.­

During the 19th century, inventors made huge strides in steam technology, leading to the development of horse-drawn steam engines. These engines used the expansion of water into steam to work the pumps powered formerly by human labor. Gasoline motors began to replace steam power in the early 1900s and, while the engines have improved a lot, the basic technology remains the same.

But how do modern water cannons actually propel so much water so far? Find out on the next page.


Water Cannon Parts

Indian police hose down demonstrators with dyed water cannons. The dye is difficult to wash off, making it easier for police to identify protesters fleeing the scene.
Tauseef Mustafa/AFP/Getty Images

Today's water cannons fulfill several different purposes. Law enforcement officials have used water cannons to disarm bombs and to control riotous crowds. Anti-riot water cannons pack enough punch to knock a person down at around 100 yards (91.44 meters), but some law enforcement organizations take the technology a step farther by lacing the water with dyes or tear gas.

Let's take a closer look at the three basic components of a water cannon: a water source, a pumping system and a deluge gun. The water source can be either a water tank that accompanies the two other components, or it can be an external source, such as a fire hydrant, swimming pool or natural body of water. Fire engines typically use both sources, allowing firefighters to begin using a tanked supply of water right away while other firefighters connect hoses to an external source. That way, there's no waiting around for water while a fire burns.


The mounted deluge gun allows the user to aim and shape the stream of water. When firefighters manually use a hose, they often have to struggle to keep it from whipping out of their control. After all, the water comes out under incredible pressure and naturally pushes the hose in the opposite direction. The deluge gun attaches firmly to the truck to prevent this, allowing one person to operate it -- sometimes even remotely.

Of course, it doesn't matter how nice the deluge gun is or how big the tank is if you don't have the necessary power. Most modern water cannons are kinetic pumps, meaning they depend on an impeller water pump to move and pressurize the water. Water enters the pump and hits the rotorlike impeller. The spinning impeller then slings the water outward, creating pressure by centrifugal force -- not unlike water in a high-speed washing machine. After the water has built up kinetic energy in the pump, it's routed out to the deluge gun. This allows for a constant, powerful stream of water.

Kinetic pumps entered the picture in the 20th century. Before that, most pumps were displacement pumps, which used plungers, pistons and gear pumps that work like enclosed water wheels.

Looking ahead, researchers in Russia are working on a way to use an electromagnetic pump to fire a stream of water. By placing a volume of liquid inside a magnetic field and then electrifying it, you can subject the fluid to the electromagnetic force, pushing it forward. Will this be the future of firefighting and crowd control? Only time will tell.

Explore the links on the next page to learn more about firefighting and water-based technology.


Lots More Information

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More Great Links


  • Bonsor, Kevin. "How Fire Engines Work." Sept. 18. 2001. (July 17, 2008)
  • Calderone, John A. "Fire Apparatus Past and Present." Firefighter Central. 2005. (July 17, 2008)
  • Hambling, David. "Russia's Ultimate Water Blaster." Wired. Aug. 20, 2007. (July 17, 2008)
  • Leibenluft, Jacob. "Purple Water Cannons." Slate. June 12, 2008. (July 17, 2008)
  • "Pump." Encyclopædia Britannica. 2008. (July 14, 2008)
  • "Water Cannon." Jaycor Electromagnetic & Electronic Systems. June 26, 2004. (July 17, 2008)
  • "Water cannon used to dismantle fake bomb." Ventura County Star. July 12, 2008. (July 17, 2008)
  • "The way we were." The London Fire Brigade. April 19, 2006. (July 17, 2008)