A footnote in the 1887 translation by George Ormsby on p 223 shows that the Biscayan is mangling an existing proverb:
Quien ha de llevar el gato al agua? (Prov. 102.) "Who will carry the cat to the water?" is a proverbial way of indicating an apparently insuperable difficulty. Between rage and ignorance the Biscayan, it will be seen, inverts the phrase.
The "Prov. 102" part refers to a running tally of "proverbs" that Ormsby keeps throughout the text:
Proverbs form a part of the national literature of Spain, and the proverbs of "Don Quixote" have always been regarded as a characteristic feature of the book. They are, moreover, independently of their wit, humor, and sagacity, choice specimens of pure old Castilian. The reader will probably, therefore, be glad to have them in their original form, arranged alphabetically according to what is of course the only rational arrangement for proverbs, that of key-words and numbered for convenience of reference in the notes.
—pp 17-18