Water

Beer is 95% water. The water you use in brewing contributes a lot to the finished beer.

Kind of.

The all grain brewer has to consider the makeup of his water, since the minerals in the water impact beer flavor during the mash. To make a perfect copy of a Pilsner Urquel, for example, the brewer might soften his water to get his water close to that in Plsen. Or harden it to make a Porter or Stout.

In the wine and spirits world, there are appellations. For instance, Champagne can only be made in one region in France. If you use the same grapes in Texas, you get Sparkling Wine, which is identical to Champagne, but not made in Champagne. Similarly, all Bourbon comes from Bourbon County in Kentucky. Everything else is whiskey.

This does not apply to the beer world. A stout brewed in Asia is very similar to a stout brewed in Dublin. Regions can give their name to beer styles, like Plsen did for Pilsener, but a pilsener can be brewed anywhere. You might have to change the chemical composition of your water, though.

For the extract brewer, it's much simpler. If the water is drinkable, it is brewable. You can filter your water to remove cholorine added by most cities, or you can boil the water to drive the chlorine out. Either way, that will improve your brewing tremendously. Some homebrewers use bottled spring water, some use tap water. My brewing partner has a well so we're using well water.