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Hose-pipe ban = use of hose-pipes is banned.
Didn't you get the memo? That's not true. Wait, now it's hyphenated too? Now what's going on?!
#hippyizalwazerite for the hosepipeumbrellafellas
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Didn't you get the memo? That's not true. Wait, now it's hyphenated too? Now what's going on?!
#hippyizalwazerite for the hosepipeumbrellafellas
The memo was fake news.
The reason for hose-pipe is the same as for motor-car, it's to correctly define what is being discussed.
"Hose" on it's own could refer to clothing, and indeed your etymological research showed the likely source of hose-pipe as referring to a tightly woven fabric cylinder for transmitting water from place to place.
Hose-pipe ban = use of hose-pipes is banned.
Hose ban = trousers are banned.
Pipe ban = a certain type of tobacco smoking (or weed, if you are a rebel) is banned.