I would think you would want the brewing water report, although it's probably worth getting a report on each, that way you know your starting point AND how well your filtration works.
If your filter ever craps out you'll also know if/how you need to treat the tap water.
Something is always fermenting....
"It's Bahl Hornin'"
Kegged: Sour Saison, Pale Ale, Aggie Ale, Firestone DBA, De Koninck Blonde
Bottled: Belgian Quad (Grand Reserve), Derangement (Belgian Dark Strong)
On Deck: Pliny the Younger