“What is the healthiest kind of water?”/“Well water.”

A water riddle is:
 
Q: What is the healthiest kind of water?
A: Well water.
 
The joke has been cited in print since at least 1976.
 
     
Google Books
Biggest Riddle Book in the World
By Joseph Rosenbloom
Illustrations by Joyce Behr
New York, NY: Sterling Publishing Company, Inc.
1976
Pg. 57:
What is the healthiest kind of water?
Well water.
 
18 July 1987, The Courier-Journal (Louisville, KY), Jelly Bean Journal, Scene sec., pg. 18, col. 8:
Q. What is the healthiest kind of water?
A. Well water.
Jennifer Rau
Louisville
     
Google Books
The Happy Camper Handbook:
A Guide to Camping for Kids and Their Parents
By Michael Elsohn Ross
Yosemite National Park, CA: Yosemite Association
1995
Pg. ?:
What is the healthiest kind of water?
Well water.
 
Google Groups: alt.humor.puns
“Puns of the Weak” 10/20/00
Stan Kegel
10/21/00
(...)
What kind of water is good to drink when you are sick? Well water
(Hunter, 8 yrs. )
 
Google Books
The Mammoth Book of Really Silly Jokes:
Humour for the whole family
By Geoff Tibballs
London, UK: Constable & Robinson Ltd
2011
Pg. 365:
What is the healthiest kind of water?
Well water.
 
Twitter
ComedyCity‏
@ComedyCityKC
ComedyCity Official Groaner Joke of the Day:
What is the healthiest kind of water?
Well Water.
Brought to you… http://fb.me/18HUQXLjo
1:04 PM - 9 Apr 2014
 
Twitter
Shanz Dev‏
@ShanzDev
What’s the healthiest kind of water?
“Well” water
#ShanzHumor 😁
9:11 AM - 15 Jun 2017