With apologies to Martin and AJ for probably butchering the science a bit...
The pH of your water is fairly meaningless - what matters is how well it is buffered, i.e. how much it resists pH change when you mix the water with the grains. Your water has a lot of carbonates in it, hence the high projected pH by the nomograph (which I am not sure how accurate that is). If you want to use that water, you might consider diluting it with RO water or using phosphoric acid to break through the buffer and drop the mash and sparge pH down.
Personally, I would use RO water. It's a great blank slate and easier to deal with.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Primary: Saison, Berliner Weisse, sLambic I, sLambic II, IPA, 70/-
Secondary: Orange Blossom Mead, Flanders Red I
Kegged: Fat Man Porter w/ 1469, Fat Man Porter w/ 005, Centennial Falcon w/ Conan, Centennial Falcon w/ Denny's, Barrel-aged Fat Man Porter, Belgian Dark Strong, Dark Mild