The water cannon at the centre of the row between Boris Johnson and Theresa May are being phased out in Germany amid concerns about their safety. The London mayor claimed he had struck a bargain with the secondhand water cannon he bought from the German federal police this week. But the two-decade old Wasserwerfer 9000 model he secured are being gradually phased out in Germany because of concerns about its safety.

The "WaWe 9" vehicle, produced by Ziegler Group and colloquially known as "Mammoth" or "Goliath" among German police, was first, introduced in 1982. It is named after the 9,000 litres it can hold in its tank, which it can spray as far as 65 metres at 18 litres a second – though some reports claim the machines can easily be adjusted to double the water pressure. Concerns about the safety of the vehicle arose first arose in 1985, when leftwing activist Günter Sare died having been stunned and then run over by a WaWe 9 during a protest march.

An investigation into his death revealed several flaws in the design of the water cannon had contributed to the accident: according to police officers, directing the jet of water at a specific target was "a matter of luck", while undimmed engine noise and a cockpit layout meant those inside had only a limited sense of what was happening outside. In 2011, the WaWe 9000 again gained notoriety when pensioner Dietrich Wagner was partially blinded by a jet of water during a protest march in Stuttgart.

Since 2010, German police has sought to replace the WaWe 9s with the Wasserwerfer 10.000 by manufacturer Rosenbauer, which would explain why London's mayor will be able to purchase his vehicles for £30,435 rather than the €1m price tag that comes with newer models.

An engineer at Ziegler told the Guardian that the vehicles sold to London would have been built no more recently than 1995 and still use old-fashioned, pre-digital technology inside the passenger cabin.