Here are just a few of the major brewing centers:
Pilzen: With an average of just 7 mg/l of calcium, this is the softest water on earth. The Bohemian Pilsner style tastes very malty, in spite of the higher hopping rates than it's sister, German Pilsner. Widely copied, this style is the gold standard and originator of the whole pilsner family.
Dortmund: The style of Dortmunder is widely misunderstood by brewers and judges alike. With calcium levels second only to Burton-on-Trent this water accents hops and presents a dry maltiness so prized in the Dortmunder style for its balance. Lingering hop bitterness, despite very low IBU's can be directly attributed to the mineral content of the water.
Vienna: While Vienna lager is prized for its malty character, it is also supposed to have a relatively dry finish with a balance of hops. This city also has very hard water similar to Dortmund. As it turns out, nearly the same water profile is available in Mexico, especially Mexico City, where many classic examples of this style continue to be made.
London: Would you be surprised to find out that this city has some very soft water? With calcium levels at about 52 mg/l it has a profile that lowers the acidity of dark malts, leaving porter very round and drinkable.