“Water separates the people of the world, wine unites them” (or, “wine brings them/people together”) is a saying of unknown origin that has been cited in print since at least 1971. The water that “separates the people of the world” usually describes the oceans.
 
The Brotherhood of the Knights of the Vine (established in 1964) has used “Water separates the people of the world; wine unites them” as a slogan.
 
 
grapestompers
T-Shirt
WATER separates the people of the world, WINE brings them together.
 
Erik Skovenborg’s Home Page: Wine Quotes
Water separates the people of the world, wine unites them. (Anonymous)
 
The Meadery
Water separates the people of the world, wine unites them.
Anonymous

Heinrichshaus: The Philosophy of Wine
“Water separates the people of the world; wine unites them.”————Anonymous
   
Google Books
Alcoholic Beverages
By Anthony H. Rose
New York, NY: Academic Press
1977
Pg. 315:
It has been said that water separates the people of the World, but wine unites them (Gates, 1971). We hope so.
 
23 June 1987, Rockford (IL) Register Star, “U.S. wine societies blossom” by John R. Hailman, pg. 2D, col. 2:
America’s officially recognized wine society on the international scene is the Brotherhood of the Knights of the Vine, headquartered in Sacramento. This group, founded in the European model but completely autonomous, belongs to the international association of such societies, and exchanges yearly visits with other chevaliers and Commanderies in Europe. Its initiation ceremony gives some idea of the spirit of the Brotherhood. After repeating the official slogan “Water separates the people of the world; wine unites them,” the initiate Knight denounces milk and water, and dedicates himself to the wines of America.
 
Google Books
Business Review
Volume 20, Issues 240-245
Thanacha: Therapatvong for Business Review
1991
Pg. 93:
At the same time, wine is also a beverage of good company. “The saying goes ‘Water separates people and wine unites them.’ Wine brings people together. It’s conducive to good humour and enjoyment of one another.”
 
20 October 1994, Syracuse (NY) Herald-Journal, “Don’t blush over wine list,” ‘94 Dining Guide advertising supplement, pg. T6, col. 2:
There is a saying: Water separates the people of the world, wine unites them.

That is, of course, if you can navigate a wine list.
     
Google Books
The Wine Spectator
Volume 20
1995
Pg. 24: 
...Byron that “water separates the people of the world, wine unites them.”
Marni Meyerson
Kearny, N.J.
   
15 November 1995, Chicago (IL) Daily Herald, “Wine from Spain maintains reputation as an affordable luxury” by Mary Ross, sec. 6, pg. 7, col. 6:
Because like I always say, “Water separates the people of the world, wine unites them.”
 
27 December 1995, Chicago (IL) Daily Herald, “Nothing loosens great thinker’s tongue like fine wine” by Mary Ross, sec. 6, pg. 4, col. 6:
Water separates the people of the world; wine unites them.
—Anonymous
 
Google Books
Romancing the Stove:
Celebrated Recipes and Delicious Fun for Every Kitchen Goddess
By Margie Lapanja
Berkeley, CA: Conari Press; Enfield: Airlift
2002
Pg. 114:
The Brotherhood of the Knights of the Vine, a “medieval” association of individuals who share an appreciation for and an interest in the vines and wines of America, holds that wine is a gift from God…and a gift from nature. The knights have as their slogan: Water separates the people of the world; wine unites them.
 
Google Books
Temecula Wine Country
By Rebecca Farnbach, Vincenzo Cilurzo and Audrey Cilurzo
Charleston, SC: Arcadia Pub.
2009
Pg. 65:
In 2002, John received a lifetime achievement award from the Temecula Valley Chamber of Commerce for his work in developing the Temecula Wine Country. He says, “Water separates people, but wine brings people together,” and “[in Temecula] regardless of what the weather is, it is a beautiful day.”
 
Selling Power Blog
11/30/2009
Lessons from a Most Memorable Meal: a Recipe for Success
(...)
At the end of the 96-page wine list you’ll find a quote from Thomas Jefferson “Water separates the people of the world; wine unites them.”