A myth demolished

Drink up. [Link]

The idea that Medieval people drank beer or wine to avoid drinking bad water is so established that even some very serious scholars see no reason to document or defend it; they simply repeat it as a settled truth. In fact, if no one ever documents the idea, it is for a very simple reason: it's not true.

Not only are there specific – and very casual – mentions of people drinking water all through the Medieval era, but there seems to be no evidence that they thought of it as unhealthy except when (as today) it overtly appeared so. Doctors had slightly more nuanced views, but certainly neither recommended against drinking water in general nor using alcohol to avoid it.

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. 

Otherwise, modern examinations of the issue are rare. In the period itself, however, there are numerous, and always uncritical, mentions of people drinking water. When Fortunatus (sixth c.) says that Radegund drank water mixed with honey, there is no suggestion at all that the water itself might be dangerous. 

Gregory of Tours (sixth c.) writes that when one man "arrived at a village by the road, he went into a small habitation and asked there for water." He even favorably mentions a pond – that is, still water – as a source of drink: "In the middle is a large pond with water that is very agreeable to drink".  And in one tale a merchant uses river water from the Saone to dilute wine. Gregory also tells of a crowd finding the marks where a hermit had knelt to drink water from the river. St. Lupicin is said to have drunk the water of a local stream. When a child restored to life miraculously speaks, he tells his mother "Run quickly and bring me a cup of water." 

When Gregory mentions miraculous cures using water associated with a holy figure, the water has more power because of that association, but he never implies that it would have been undrinkable otherwise: "Since then a great number of the sick, after having drunk water or wine into which this gem had been plunged, were immediately restored to health.”; "Water left there by the rains is sought by the sick, who recover their health when they have drunk it.”; "Often the possessed, the feverish and other sick people recover their health in drinking water from this well".

  

It was not unusual in speaking of the devout or the saintly to say that they drank mainly water. Gregory says of a boy who received religious training that he became "so abstemious that he ate barley instead of wheat, drank water instead of wine, used an ass instead of a horse, and wore the meanest garments."  Patroclus, a hermit in Bourges, drank only water “a little sweetened with honey” Other writers share similar incidents. St. Paul Aurelian dipped his bread in water. A life of St. Clothilde tells how she brought a cup of spring water for builders at Les Andelys (only to have it changed to wine).