Boris Johnson has agreed to be blasted by a water cannon to prove they are safe, after he controversially bought three for the Metropolitan Police at a cost of £218,000.
He told LBC radio on Wednesday morning: "Man or mouse. You've challenged me, so I suppose I'm going to have to do it now."
He told presenter Nick Ferrari: "I can see all my press people pulling their hair out over this, but never mind, it's got to be done. Thanks for that one."
On Tuesday it was revealed Boris had ordered the purchase of three water cannon - even though home secretary Theresa May has yet to agree they can be used.
Water cannon have never been used on the British mainland, although they have been deployed in Northern Ireland. The mayor has bought the three water cannon from the German federal police.
In February a German pensioner, blinded by a police water cannon, addressed a public meeting in London.
Dietrich Wagner was left unconscious, his eyes irreparably damaged when he took the full force of a water cannon to the face during an environmental protest in Stuttgart.
He warned: "Ever since I was hit my life has drastically changed. I can’t drive, go shopping, read or do any of the things I used to do. My message is police need to be aware that they are not just a big shower, they are lethal weapons and do serious bodily harm."
His eyelids were torn by the force of the water, damaging the lenses of his eyes and fracturing his orbital bone around the eye.
Labour and the Liberal Democrats have condemned the water cannon purchase as "reckless", insisting there is not enough evidence that the tactic is effective in maintaining order.
Caroline Pidgeon, Liberal Democrat leader on the London Assembly, said: "There is no evidence to defend the provision of water cannon in London.
"After three hearings at City Hall the case against the use of water cannon was compelling. London Assembly Members, across the political parties have expressed their total opposition to one of the worst aspects of European policing being adopted in London. The Mayor's refusal to listen or engage with evidence presented to him is shameful."
Met commissioner, Sir Bernard Hogan-Howe, has pledged that water cannon would be "rarely used and rarely seen".