OK, finally found the conduit to people who actually know what they’re talking about and have investigated this issue.
Paolo Squatriti is a rare writer (in Water and Society in Early Medieval Italy, AD 400-1000) to look at this question. He writes of both Italy and Gaul:
“Once they had ascertained that it was pure (clear, without odor, and cold) people in postclassical Italy did, in the end, drink water. Willingness to drink water was expressed in late antiquity by writers as dissimilar as Paulinus of Nola, Sidonius Apollinaris, and Peter Chrysologus, who all extolled the cup of water.”
In Misconceptions About the Middle Ages, Stephen Harris and Bryon L. Grigsby write: “The myth of constant beer drinking is also false; water was available to drink in many forms (rivers, rain water, melted snow) and was often used to dilute wine.” Steven Solomon’s Water: The Epic Struggle for Wealth, Power, and Civilization examines uses of water, including for drinking, going back to Sumeria.
OK, finally found the conduit to people who actually know what they’re talking about and have investigated this issue.
Many other quotes from historical figures showing that water was a widely accepted and consumed beverage. I’m sold.