What does it mean to call someone a 'drink of water'?
Solution 1:
Meaning (of "long drink of water") is ambiguous, just generally meaning "tall", as reflected in answers here, though specific use can have connotations of "tall and attractive (man/woman)" or "lanky, gangly" (tall and awkward).
The origin appears to be Scottish, dating to Scots lang drink (1887), as suggested by the 1924 quote from Mo Nickels (MetaFilter), quoted by Little Eva.
The Dictionary of the Scots Language cites (at drink and lang):
The life and recollections of Doctor Duguid of Kilwinning, John Service, 1887, p. 103: “Stair had grown up into a great lang drink, and would faukled, as Robin Cummell said, if he fell.”
(I've put this at long drink of water at Wiktionary for reference.)
Solution 2:
In the linked clip from The Shawshank Redemption, Morgan Freeman's character Ellis Boyd 'Red' Redding refers to the "new fish," Andy Dufresne, as a "tall drink of water with a silver spoon up his ass." The "tall drink of water" part of this phrase is not derogatory or insulting and simply means that Dufresne is a tall, slender man.
The second half of the phrase---with a silver spoon up his ass---is, however, definitely meant to be denigrating and can be taken to mean that Andy Dufresne is a spoiled rich-boy, who's been raised in the "lap of luxury" or privilege. You see, 'Red' Redding is a downtrodden convict who is not---at first blush---terribly impressed with Andy Dufresne, whom 'Red' considers to be a "lightweight" who won't last very long in the rough environs of the Maine State Penitentiary. 'Red's' evaluation of Andy is dead wrong, of course, as time will tell.
More generally---that is, outside of this film and the penitentiary---the phrase is highly complimentary because, sometimes, there's nothing quite so pleasing or desirable to a gal as a, "tall drink of water!" (Thanks, KL.)
Tall drink of water
A man or woman that is tall, gorgeous, and super delicious. Like on a hot day, a tall drink of water is absolutely appealing.
Old slang for a visually appealing man or woman.
"Would you look at hunky man? He is one tall drink of water. I could drink that RIGHT up." see, The Urban Dictionary tall drink of water
I found the following etymological information online but cannot attest to its accuracy:
The term exists in two forms: long drink of water and tall drink of water. Most dictionaries do not have the expression and no dictionary I checked has any speculation about the etymology of the term. The Historical Dictionary of American Slang defines the term as "a tall man" and has a first citation of 1936, but with minimal effort I've been able to antedate it possibly to 1904, though it's not a strict use of it in metaphor:
1904 Daily Huron (South Dakota) "Makes a Big Hit" (May 7) p. 3: Then there is baby Patti, who is not much larger than a long drink of water and who is a marvel for a child.
The earliest for certain citation I have is this.
1924 Times (London, England) "The Speaker Defied" (May 10) p. 12: Mr. Kirkwood addressed his reproof to Lord Winterton, who, along with his colleagues, had protested against the defiance of the speaker's ruling. "Ye are not treating with Indians, ye big long drink of water," he shouted. Immediately the Speaker reproved the member for Dumbarton.
Another newspaper that quoted the same thing indicates that the speaker, Kirkwood, is a Scottish Labor party member, as also indicated by the "ye." There's nothing about the expression in the Dictionary of Scots Language.
posted by Mo Nickels, from Ask Meta Filter tall drink of water
Red Redding and his "Tall Drink of Water"