22 May 1982 — UPI wire, Sacramento. Robert Crabbe’s story on California’s Proposition 9 canal fight runs under the headline “‘Whiskey Is To Drink. Water Is To Fight Over’ — Mark Twain.” Outside QI’s trail and eleven months earlier than it. The Twain credit is in the headline only; the copy beneath never names him.
12 April 1983 — Aberdeen American News, South Dakota. QI’s earliest located instance, spoken by a government-agency head named Warren Neufeld and, by QI’s reading of the context, used as an anonymous adage. No Twain, no author at all.
Summer 1983 — Western Wildlands: A Natural Resource Journal, Montana. The first appearance QI records that credits Mark Twain, and the first in the now-familiar “water is for fighting over” form.
September 1983 — Wall Street Journal. Credited to Twain again, in a shortened wording.
1984–85 — the saying goes national. A U.S. House hearing (Governor Bruce Babbitt), the New York Times, the San Diego Union, a Resources for the Future annual report and the Philadelphia Inquirer all carry it — sometimes credited to Twain, sometimes attributed only to “Westerners” in general.