You would probably want to add gypsum or Calcium Chloride for many beers to help lower pH with the Ca addition, and add the SO4 and Cl flavor ions. That assumes you brew all grain. For extract I would use RO or distilled, as that water may give you an Alka Seltzer beer.
Some small breweries around here use a lot of phosphoric acid to drop the alkalinity. That would work even better for you, as the other ions are low, and the Na and Cl are high around here.
What general area are you in, or what is the local geology like?