Big gun G20 cops have up their sleeve The water cannon truck garaged at the Brisbane Showgrounds. IT'S the photo police didn't want you to see. Parked in a garage at the RNA Showgrounds, the armoured truck has a water cannon that will be used on demonstrators if G20 protests turn violent. MEDIA CENTRE: Banned animals brought in PROHIBITED: List of banned people grows NO ACCESS: Full list of road closures The $600,000 truck - brought in from NSW - can carry 12,000 litres of water and its blast is capable of knocking people from their feet. It was bought before the 2007 APEC summit and has been brought to Queensland because of violence that has marred previous G20s, notably in Toronto. Police officers guarding vehicles at the showgrounds swooped when The Courier-Mail took photographs of the truck from a public footpath yesterday. Photographer Adam Armstrong said four officers detained him for more than 20 minutes and threatened to confiscate his camera and delete the images. He was released only after the officers consulted senior police and Armstrong called a lawyer. A Queensland Police Service spokesman said: "Police take the integrity of methodologies they use seriously. It is important to protect these methodologies to ensure policing tactics aren't compromised in an operational situation. For security reasons, officers may ask anyone in or near the restricted area to verify their details.