The Met Police is wasting nearly £22,000 a year servicing three unused water cannon bought by ex-mayor Boris Johnson.
In response to a Freedom of Information request, the force admitted that maintaining and storing the second-hand equipment costs £21,866 annually.
Mr Johnson bought the second hand cannon from Germany for more than £200,000 two years ago to cope with events like the London riots, only to see their use blocked by then Home Secretary Theresa May.