Water is the most basic and fundamental ingredient in all beer, accounting for the vast majority of the beer's overall volume. While for the most part water is simply the base ingredient into which the others are added, the presence of trace minerals such as gypsum or iron will have a potentially drastic effect on the final flavor of the beer. Trace minerals in small amounts are also important yeast
nutrients, and water lacking these (such as distilled water) causes fermentation problems when used in brewing.
Regions have water with different mineral components; as a result, different regions were originally better suited to making certain types of beer, thus giving them a regional character. For example,
Dublin has hard water well suited to making stout, such as Guinness; while Pilzen has soft water well suited to making pale lager, such as Pilsner Urquell. The waters of Burton in England contain gypsum, which benefits making pale ale to such a degree that brewers of pale ales will add gypsum to the local water in a process known as Burtonisation.