When travelling in Europe, a few campsites which have fully serviced pitches, use an strange connector for the water. Generally you can borrow one which adapts to the standard thread etc. but I'm always a bit concerned one isn't available etc.
The fixed end (female) is a hole, may be 8 mm in dia. There is sometimes a button to release the male part, which looks very like a PCL connector (as used in air compressors etc).
Sometimes the PCL part is connected to a short hose and perhaps a 'hoselock' style connector, others an inline tap like you see for a washing machine, .....
Unfortunately, I've never measured one on site- no least as I don't carry calipers etc. on holiday.
Has anyone seen such a thing in the UK and know the name/make, please?