A humorous alteration of au revoir¹ after the noun reservoir, the exclamation au reservoir is first recorded in Little Pedlington and the Pedlingtonians (London, 1839), by the English author John Poole² (1786-1872):

“I’ll call and just say ‘how d’ye do?’—Well, good bye! Shall see you in the Crescent this evening, of course—promenade, you know—man with the drum and the pandean pipes plays from seven till eight—all the world will naturally be there. Au reservoir.”

¹ French au revoir means goodbye until we meet again. It translates, literally, as to the seeing again—cf. Romanian la revedere, literally to the seeing again, and Italian arrivederci, or a rivederci (from a, meaning until, rivedere, to see again, and ci, us).

² about John Poole, cf. also meaning and origin of ‘Mrs Grundy’, meaning and origin of ‘Paul Pry’ and origin of ‘all my eye and Betty Martin’

On Thursday 17^th October 2002, the Missoulian (Missoula, Montana) published Ouiiiiiiii, the review of The Transporter, an English-language French action film, review in which Bryan Di Salvatore wrote:

The movie takes place in France. France is a country in Europe famous for many things.
One thing is a variety of cheeses.
Another thing is wine.
Another thing is letting cats walk freely through the dining rooms of restaurants.
Another thing is letting dogs poop on the sidewalks.
Another thing is disobeying smoking laws.
Another thing is not fighting very well in your major wars.
It is a very beautiful country that has both snow-covered peaks and warm, beautiful beaches.
Charles de Gaulle was French.
English is not France’s native language. It is French.
To speak French, take a regular American word, like Havre, and don’t pronounce about half the consonants. In the case of Havre, which should be pronounced like it looks, say “Haa.”
Isn’t that the stupidest?
To spell in French, add several vowels to the correct spelling. Take the capital of Alaska³.
Another thing to remember when speaking French is to use your hands a lot. Not as much as you do when speaking, say, Italian, or Macedonian, but a lot more than speaking English or Slovenian or Norwegian. I was going to say Finnish, but nobody in his right mind speaks Finnish, or rather Finlandish.
If you don’t use your hands when speaking French, French people will mock you right to your face and make pouty faces and treat you and your loved ones with extreme contempt.
[…]
Au reservoir, mis bons amis.

³ capital of Alaska: Juneau, named after a gold prospector from Quebec, Joe Juneau

In the comic strip Gasoline Alley, published in the Argus Leader (Sioux Falls, South Dakota) on Monday 15^th June 2001, Jim Scancarelli made Mr. Pye say au reservoir to Mrs. Wallace: