A bowser is a generic name for a tanker of various kinds.
The term bowser is used by water companies in the United Kingdom to refer to mobile water tanks deployed to distribute fresh water in emergency situations where the normal system of piped distribution has broken down or is insufficient. The term rose to prominence in general usage in England in July 2007 when severe flooding in the valley of the River Severn caused interruption of the piped-water supply to a large area of Gloucestershire.
Bowser also describes a fuel tanker used to deliver fuel to aircraft at airports or airfields. The term also describes refuelling boats that supply seaplanes. The term also describes vehicles that fill heavy construction equipment such as hydraulic excavators and bulldozers.
The related verb, "bowsing", is used in the fuel distribution industry to refer to the practice of customers of one fuel distributor to be able to collect fuel from a depot (including retail stations) of a second fuel distributor, at the prices of the first distributor. As such, it is a method of mutual distribution, improving fuel access for customers while reducing the main costs of each distributor. Being a commercial service, it normally applies to DERV (road vehicle diesel fuel) rather than petrol (gasoline).
At the former nuclear research facility at Dounreay in the far north of Scotland, the word bowser is used to describe various moveable (but not wheeled) vessels that contain alkali metals (sodium or NaK), protected from oxidation by an inert gas. The word may also have been in use at the Atomic Energy Authority's (now UKAEA's) southern sites.