When I first seen this I thought it was from Manchester, where I last seen one like it.
I was able to chat very briefly with the driver, who told me he was on his way to Ireland from Southampton, to fill steam engines with water. This appliance is no longer owned by any local brigade
H20BTT seen at Holyhead, 18.6.15.
Picture added on 03 September 2015 at 16:46