The affects of water on beer should not be underestimated, the minerals and various "salts" contained in water from a specific area can change the entire character of beer, the same recipe made with water from two different places can make such a profound difference that the resulting beers have sometimes been sold as two completely different beers.

One of the most famous examples is "Burton upon Trent". In the late 1700's maltsters began to use coke ovens to dry and roast their malts, this made Pale Ales possible for the first time and most brewers began to produce them. In the breweries of Burton on Trent they also began to produce pale ales but these tasted completely different from their counterparts in other areas of the country. Drinkers liked the Burton product and in a fairly short time it became the source for the premier pale ales of the time. They held their lead for years until a chemist finally managed to re-create the salts in the Burton water. Burtonizing is still a term used for the treatment of water to produce the tastes preferred for pale ales or bitters.

Water makes up more than 90% of beer so the qualities of water are very important, fortunately almost any water can be treated today to give the tastes that brewmasters are looking for. It's easier and cheaper if the natural water matches the profile they need but no longer essential.

Water can cause a salty taste from some of the minerals in it and, although this does not sound desirable, in some styles it is almost essential.
Metallic tastes can also be caused by the mineral content of water but this taste is not usually wanted in beer. You never know what some clever brewmaster might come up with to make use of these tastes however.
"Phenolic" is another taste which can come from water. This is the clove or sometimes smoke like taste in some beers, although it is more common to get these tastes from the yeast. Too much of this taste or in the wrong combinations and it can take on a medicine or hospital smell.

Water and the minerals and salts it contains are critically important to the brewmaster. It is the first consideration in terms of what style of beer he will make. With treatment he can create the water he needs for any style of beer but this is still the essential first step.