A water cannon is a device that shoots a high-velocity stream of water. Typically, a water cannon can deliver a large volume of water, often over dozens of meters. They are used in firefighting, large vehicle washing, riot control, and mining. Most water cannons fall under the category of a fire monitor.
Firefighting
Water cannons were first devised for use on fireboats. Extinguishing fires on boats and buildings near the water was much more difficult and dangerous before fireboats were invented. The first fireboat deployed in Los Angeles was commissioned on 1 August 1919. The first fireboat in New York City was Marine 1, deployed 1 February 1891. There may have been other fireboats elsewhere even earlier.
Fire trucks deliver water with much the same force and volume as water cannons, and have even been used in riot control situations, but are rarely referred to as water cannons outside this context.
Riot control
The first truck-mounted water cannon was used for riot control in Germany in the beginning of the 1930s.
The most modern versions do not expose the operator to the riot, and are controlled remotely from within the vehicle by a joystick. The Austrian-built WaWe 10.000 by Rosenbauer used by German police can carry of water, which can deploy water in all directions via three cannons, all of which are remotely controlled from inside the vehicle by a joystick. The vehicle has two forward cannons with a delivery rate of , and one rear cannon with a delivery rate of
Water cannons designed for riot control are still made in the United States and the United Kingdom, but most products are exported, particularly to Africa and parts of Asia such as Indonesia.
Safety
Use of water cannon in riot control contexts can lead to injury or death, with fatalities recorded in Indonesia (in 1996, when the cannon's payload contained ammonia), Zimbabwe (in 2007, when the use of cannons on a peaceful crowd caused panic), Turkey (in 2013, when the payload was laced with "liquid tear gas"), Ukraine (in 2014, with the death of activist and businessman Bogdan Kalynyak, reportedly catching pneumonia after being sprayed by a water cannon in freezing temperatures) and South Korea (in 2016, when a 68-year-old farmer died after injuries sustained by a water cannon the previous year). Water cannons in use during the 1960s, which were generally adapted fire trucks, would knock protesters down and on occasion, tear their clothes.
On 30 September 2010, during a protest demonstration against the Stuttgart 21 project in Germany, a demonstrator was hit in the face by a water cannon. Dietrich Wagner, a retired engineer, suffered damage to his eyelids and retinas, resulting in near-complete loss of his eyesight. Graphic imagery was recorded of the event, sparking a national debate about police brutality and proportionality in the use of state force.
According to a report issued in the United Kingdom, using plastic bullets instead of water cannons was justified because the latter "are inflexible and indiscriminate", although several people had previously been killed or seriously injured by plastic bullets.
Media effect
The presence of the media at riots has had a significant impact on water cannon use. There is much pressure on police departments to avoid bad publicity, and water cannons often play badly in the press. It is considered that this is a likely reason that they are not used more often in some countries.
Confrontations that took place in the era of the American Civil Rights Movement, where water cannons were used by authorities to disperse crowds of protesting African Americans, has led to the demise of water cannons in the United States.
Alternative payload
Dye
In 1997, pink dye was reportedly added to the water used by South Korean and Indonesian police to disperse a riot. The implication is that they might use this mark to make it easier to arrest rioters later. The United Kingdom, which had sold the water cannon to Indonesia, condemned this practice (although the Royal Ulster Constabulary had used a water cannon with purple dye during The Troubles in Northern Ireland) but later approved the sale of further water cannons to them. Most modern water cannons are also capable of adding tear gas to the stream.
Electrified water jet
In 2004, Jaycor Tactical Systems was experimenting with additives (salt and additives to reduce the breakup of the stream into droplets) that would allow electricity to be conducted through water. They have demonstrated delivery from a distance of up to , but have not yet tested the device on people.