Why do police douse protesters with colored water?

As Egypt prepares to mark the first anniversary of the Egyptian revolution on Wednesday, with activists mapping out protest routes and the ruling military council partially lifting the country’s emergency laws and releasing prisoners in apparent goodwill gestures, Al-Masry Al-Youm is reporting something rather odd. Anonymous security sources tell the Egyptian newspaper that security forces are planning to use batons, loudspeakers, and “colored chemicals that will stain one’s skin for six months” against “those perceived to be violating the law.”

It’s the colored chemicals in particular that’s gotten picked up by Twitter users in Egypt, generating a mixture of outrage (“colored chemicals you idiots?!!!!!), humor (“so it’s paint ball fight now?”), advice (“Vaseline reduces the effects of colored water”) and skepticism (“if it’s real we wouldn’t be finding out about it a week beforehand”). Several people have tweeted this footage of Ugandan police using water cannons to spray opposition activists with pink dye in Kampala in May, after rising food and fuel prices sparked “walk to work” protests.

According to Maki Haberfeld, chair of the Department of Law, Police Science, and Criminal Justice Administration at John Jay College of Criminal Justice in New York, injecting semi-permanent, bright-colored dyes into water cannons is a relatively cheap and nonviolent way to identify and detain rioters after crowds disperse and deter demonstrators who worry about staining their clothing or skin. “Water is considered to be benign but at the same time people don’t want to be sprayed by water and especially colored water,” she explains. “So it’s not a bad alternative.” But Haberfeld adds that modern police departments aren’t likely to use such a low-tech tactic.

Nevertheless, the approach is still employed frequently. The most famous use of colored-water cannons took place in South Africa in 1989, when police soaked anti-apartheid activists with purple water and one protester turned a water cannon back at police and government buildings, giving birth to the anti-apartheid slogan “the purple shall govern.”

But there are more recent examples (including blue water cropping up in a confrontation between squatters and South African police last May). Photos and videos online capture colored-water cannons dispersing protesters everywhere from Argentina to Malaysia to Hungary, and Israeli police have used colored water on protesting Palestinians (see above) and Jewish settlers in the past several years (the water aimed at settlers being evacuated from Gaza also contained turpentine). Some British lawmakers suggested tagging looters with dye during the London riots last year. And, as the pictures below of Kashmiri government employees protesting in Srinagar in 2008 and 2011 attest, Indian police appear to be particularly fond of purple water:

When supporters of ousted Honduran President Manuel Zelaya took to the streets of Tegucigalpa in 2009, meanwhile, they were hosed with red liquid:

Sid Heal, a retired commander with the Los Angeles Sheriff’s Department and riot-control consultant, says red dye isn’t the best because it can be mistaken for blood. And he adds that dyes can also be mixed with pepper spray or delivered through sophisticated projectiles. “If you see someone lighting a building on fire, you can hit them with the dye and record the incident,” he explains. “And then if you find the person, you can connect them back to the projectile and prosecute them.” This past summer, David Hambling noted at Wired that some dye tactics are actually quite high-tech:

A more subtle approach is to use invisible dye that only shows up under UV light, a technique used for marking suspected insurgents in Afghanistan. UK company Smartwater goes even further, with invisibly coded sprays which can record exactly where a suspect was sprayed. These provide solid forensic evidence for a prosecution.

But dyes have their drawbacks too. When Kashmiri protesters stared down purple water in 2008, Slate pointed out that innocent bystanders had been hit by the spray and some locals were complaining that the dye was toxic. “The technology by itself doesn’t provide a solution,” Heal argues. “It has to be incorporated into a plan to identify suspects.”

Additional photo credits: Tauseef Mustafa/AFP/Getty Images; Rouf Bhat/AFP/Getty Images; Orlando Sierra/AFP/Getty Images