You must have seen photos of protesters being doused with colored-water cannons by the police. Using water canon is understood as it’s an easy non-hazardous way to disperse mob, but why would police spray protesters with purple and pink water? Simple: to identify and arrest them later. Many water cannons on the market today come with a tank specially designed to store a semi-permanent colored dye. If police decide they want to "tag" protesters with the dye, they can press a button to inject it into the main water stream. Once the water cannon is trained on a crowd, anyone hit by the spray will be easily recognizable by police.
The most famous use of colored-water cannons took place in South Africa in 1989, when police soaked anti-apartheid activists with purple water. But in the ensuing chaos, one of the protester turned a water cannon back at police and towards the local headquarters of the ruling National Party. The headquarters, along with the historic and white-painted Old Town House, were doused with purple. The next day, a graffiti artist tagged the Old Town House with the phrase "The Purple Shall Govern," which soon became an anti-apartheid slogan.
Police spray Ugandan opposition party leaders with colored water during demonstrations in the capital Kampala, May 10, 2011. President Yoweri Museveni has vowed to crush the protests and blamed rising food and fuel costs on drought and global increases in oil prices. (James Akena / Reuters)
During the last 15 years, protesters in Hungary, Indonesia, Argentina, Malaysia, India and Israel have all been showered with colored water. In Uganda last year pink dye was employed to humiliate protesters. In Israel, Palestinian rioters were sprayed deep blue, the colour of the Israeli flag. The Hungarian police use green, the Koreans orange. Indian police is particularly fond of purple.
Police use a water cannon during a demonstration on the streets of Dhaka, Bangladesh, April 5, 2011. (Shuvo Das—Demotix/Corbis)
A man holding a Palestinian flag is sprayed by Israeli police during a protest in the West Bank village of Bilin, August 18, 2006. (Abbas Momani—AFP/Getty Images)
Indian policemen fire purple colored water from a water cannon on Kashmir government employees during a protest on April 06, 2011 in Srinagar. (Yawar Nazir—Getty Images)
Demonstrators are sprayed with a water cannon by Israeli border police during a protest against Israel's separation barrier in the outskirts of the village of Bil'in, near the West Bank town of Ramallah, August. 18, 2006. (Nasser Shiyoukhi—AP)
Riot policemen use water cannons to disperse thousands of protestors during a demonstration, October 23, 2006, in central Budapest, as Hungary commemorates the 50th anniversary of its 1956 anti-Soviet uprising. (Joe Klamar—AFP)
Police shoot water cannons as Jammu Kashmir state government employees shout anti government slogans during a protest outside the civil secretariat in Srinagar, India, May, 5, 2008. (Dar Yasin—AP)
Riot police fire water cannons towards protesters during a rally against U.S. President George W. Bush's visit on August 5, 2008, in Seoul, South Korea. (Chung Sung-Jun—Getty Images)
Ugandan opposition politician Olara Otunnu is shielded by his supporters during an attack with water cannon by Ugandan police after he refused to stop his protest march through central Kampala, May 10, 2011. (Marc Hofer—AFP/Getty Images)
Anti-riot police officers use colored water to disperse opposition supporters in the Kireka area on the outskirts of Kampala on August 17, 2011. Ugandan police fired teargas and water cannon to disperse opposition supporters who had gathered in a Kampala suburb on Wednesday to mourn people killed during demonstrations earlier this year, witnesses said. (James Akena / Reuters)
Police spray Ugandan opposition party leaders with colored water during demonstrations in Kampala. (James Akena / Reuters)
Kashmiri government employees are sprayed with purple colored water by Indian police to disperse a protest in Srinagar on May 9, 2012. (Tauseef Mustafa / AFP - Getty Images)
Indian police in Srinagar on May 9, 2012 used a water cannon and batons to disperse hundreds of government employees while detaining dozens as they attempted to reach the civil secretariat. (Fayaz Kabli / Reuters)