Untitled (Boris Johnson Water Cannon), 2016, Ed. 3

Study for Untitled (Boris Johnson Water Cannon), 2016, ed. 3, est. £35,000-£43,000. installation image from Longmoor Army Camp: Andrew Matthews/PA via Guardian

[UPDATED] I am pleased to announce that three works will be coming up for sale in London. Details will be forthcoming from the Greater London Authority, who may have some particular requirements for bidding, but I am confident that seasoned art collectors will be welcome. So watch this space.
The work, Untitled (Boris Johnson Water Cannon) (2016), comprises a c. 1990 Ziegler Wasserwerfer 9000, or “WaWe 9” water cannon, with 9,000-liter capacity, originally owned by the German federal police, converted to UK specifications, and modified at considerable expense with: CCTV, warning equipment, 999 sirens, and stereo/CD player. It exists in an edition of three.
The Wasserwerfer 9000s shown here are two of the six operated by the Police Service of Northern Ireland, and are not necessarily representative of the livery or accessories of the water cannons which comprise this work. They were used for training Metropolitan Police. So perhaps they should be considered studies. image: Stephen Barnes/Alamy via Guardian
Oh, here’s one of the actual pieces, as seen in a tweet from former Deputy Mayor for Policing Stephen Greenhalgh. They were unannounced and hidden, but the BBC located two of the three editions in Gravesend and filmed them via drone.
Untitled (Boris Johnson Water Cannon) and unidentified paintings by Lucien Smith (?) installed at Gravesend, 2016. image: bbc
It looks like they were installed alongside some fire extinguisher paintings by Lucien Smith, which seems appropriate. Definitely putting that group show on the CV.
Rain Painting, Lucien Smith, via moranbondaroff
While Untitled (Boris Johnson Water Cannon) may be exhibited publicly or privately, it is the artist’s intention that it not be deployed in any capacity against any living thing. They may be used for painting, though. Any resulting works, installations, performances, video, or other materials will be evaluated and certified in consultation with the U(BJWC) owner and/or curator on a case-by-case basis.
cf., Purple Rain Protest, Cape Town, South Africa, 1989, image: via

[AUG 2019 UPDATE] The original sale of the water cannons by the German federal police restricted their sale “to a European policing or civil protection organisation, as a guard against them being used by a repressive regime,” as the Guardian reported in November 2018.  That is when, after two years of unsuccessful attempts to find a police buyer, the GLA sold them for £11,025 to a scrap metal yard in Nottinghamshire. That outfit, Reclamation Ollerton (LTD) was planning to dismantle the cannons and export the parts.

The next day the BBC reported that the Museum of London was interested to acquire parts of the cannons. “Whether it’s possible to salvage a part of the water cannon from the scrap yard has yet to be determined, but even a section of it could help to tell a complex story about policing in the capital, which forms an important part of our collection,” said a museum spokesman who did not explain what, if anything, the museum had attempted to do to acquire the cannons in the intervening years. [Though I grant I’m not the most credible person to be calling anyone out for sleeping on these things as objects.]

Boris Johnson’s unused water cannon had £1,000 stereos fitted [theguardian]
Water cannon bought by Boris Johnson to be sold off without being used [theguardian]
Previously, related:
Police Action Painting
Protestors’ Folding Item, 2014