Well Drink

A “well drink” means any house liquor that is conveniently located in a bartender’s well. A call drink is where a customer requests a brand name for his or her drink. Well drinks are usually slightly cheaper than call drinks.
 
Both “well drink” and “call drink” have been cited in print since at least 1968.
 
   
Wiktionary: well drink
Etymology
From the well near the bar (and thus handy to the bartender) holding bottles of liquor.
Noun
well drink (plural well drinks)
1. A mixed drink for which one does not specify the exact brand of liquor to be used.
 
3 May 1968, The News (Van Nuys, CA), “Tab West Valley Hyatt for Warmth, Quality Foods,” pg. 30-A Central, col. 7:
He points out that every Thursday and Saturday is “Ladies Day” and that Mondays through Saturdays, between 5 p.m. and 7 p.m. name brand “well” drinks are served at a reduced price.
 
5 May 1968, The Arizona Republic (Phoenix, AZ), pg. 8-N, col. 4 ad:
ALL WELL
Drinks
60c
(Cimbers Theatre Restaurant—ed.)
 
14 August 1968, Bakersfield (CA) Californian, pg. 8, col. 7 ad:
All Well Drinks 50c
(Sugar Loaf Lodge—ed.)
 
3 February 1970, San Diego (CA) Union, pg. D-4, col. 4 classified ad:
PAL JOEY’S IS MOVING
(...)
Early wkend swinger 7:30-8:30 all well drinks 45c.
 
9 April 1971, Chicano (Colton, CA), pg. 3, col. 1 ad:
ALL WELL DRINKS & BEER 50c
(The Silver Queen—ed.)
 
Google Books
San Diego Magazine
Volume 32
1980
Pg. 38:
Happy Hour Tues. thru Fri. 4-8; drafts 10 cents, well drinks 65 cents and call drinks 90 cents.
 
3 May 1981, The Sun (Baltimore, MD), “Right words to use when ordering your booze‎” by William Safire, pg. D4:
“A call drink Is any drink where the customer names the liquor by brand name; a well drink is any drink using the liquor of the house. ‘What do you have in the well?’ means ‘What house liquor do you carry?’”
 
11 September 1981, San Diego (CA) Union, pg. B-11, col. 4 ad:
All Well Drinks $1.00 All Call Drinks $1.25
(Daisy’s—ed.)
   
Anchorage (AK) Daily News
A neat guide to bar terms
Published: February 13, 2008
By Jessica Bowman
(...)
Well drink: A liquor and a mixer without a defined brand.
Call drink: To request a brand-name liquor (Ketel One, Grey Goose) instead of the house. Supercall means to ask for the best brand the bar carries.
 
To Serve Mankind
August 3, 2008
Bar and Restaurant Lingo
(...)
Call – refers to a named spirit used in a drink; above the well liquor.  Absolut is a typical call vodka, whereas some cheap swill like Popov would be the low-budget well vodka in the speed rack.
(...)
Well – the generic liquor used in a basic drink.  If one orders a vodka collins, the well liquor will be used.