What drink was often safer than water in medieval towns?

The story behind the answer

In crowded medieval towns, wells and rivers were often contaminated by waste. Brewing involved heating the mash and a short boil, then fermentation that lowered pH and added a bit of alcohol—conditions hostile to many pathogens—so the resulting low-strength “small” brew was safer than raw water and drunk all day, even by children.

Wine was costly and region-specific, mead required scarce honey, and cider was seasonal and less common in many regions. Grain, by contrast, was ubiquitous, so households, inns, and monasteries brewed constantly; some urban workers even received daily rations as part of their pay. In the late Middle Ages, hopped versions spread from the Low Countries, but both hopped and unhopped grain brews served as everyday hydration.