These are high high-pressure systems that shoots jets of water, sometimes mixed with chemical irritants or dye, over dozens of metres. The power of the water jet can knock a person over, push people into fixed objects, or pick up loose objects and propel them as missiles. They are often mounted on crowd control vehicles, but they can also be mounted on buildings or carried as a backpack.
They are designed to be used to disperse crowds, keep crowds at a distance, and support police cordons. However, In the context of a public gathering, any use of water cannon will affect all people in the vicinity, creating a high likelihood of affecting bystanders. Even when targeting those engaged in criminal activity, use of water cannon risks causing them disproportionate harm. In addition, if they contain a mixture of water and chemical irritants, it impossible to deliver accurate and targeted doses of the irritant. As such, they are indiscriminate and potentially harmful. Water cannon should never be used at sub-zero temperatures as the water can cause hypothermia and frostbite.
Any use of water cannon must be in-line with international human rights standards and they should never be used to disperse a peaceful protest.
