Hop alpha acids........what part ,if any, do they play in bittering/aroma? In looking at the varieties the relationship is not clear to me.....
Water source/type.......how much of a role does this play in the type/quality/taste.......?
Used to play a role in the pimping of the product...ie Olympia....artesian water......etc.
juantanamera gave a pretty good answer. I'd add that when the IBU's (International Bittering Units) of a beer are calculated it is based on the alpha acid of the hops. The alpha acid is listed as a percentage. Alpha acids are extremely important to the bitter profile of a beer.
If you're looking for expert opinion, consult Charlie Papazian's 'The Complete Joy of Homebrewing' or John J. Palmer's 'How to Brew.'
If you want the short, non-expert answer, here goes:
Alpha acids are the bittering component of hops. The hops typically used in modern, West Coast style IPA and double IPA are full of alpha acids. Hop varieties traditionally used in English and German beers have less alpha acids. During brewing, the wort (unfermented beer) is boiled for an hour or more. The hops added at the beginning of the boil provide bitterness but no flavor; those added at the very end, aroma and flavor but not bitterness; hops added in the middle of the boil give some of each. Different varieties of hops have different aromas - floral, spicy, citrus, pine are some common descriptors.
Water is historically important in brewing beer because the mineral content, or lack there of, affects the beer in various ways. It's not really important in modern brewing because it's quite simple to filter the water or to add minerals as needed. So brewers can have whatever type of water they need, wherever they brew.