I'd say 1.5 - 2 cups of water should be plenty. I added 4 oz of maltodextrine to a bitter once that finished too low. Worked really good and I feel like it saved the batch.
Primary #1:Dunkel #2:Empty
Secondary #1: Peach Rhubarb Wine #2: Empty #3: Empty #4: Sparkling Elderflower Wine
Kegged: Piker Liker Porter, Umlaut my Kölsch V
Bottles: Big 50 Barleywine, Framboise Lambic, Red Rye IPA, Dark Belgian Strong, Belgian Golden Strong, Kicked by a Moose Scotch Ale, Apfelwein, Russian Imperial Stout, Carmelite Tripel, Rhubarb Wine, Barolo Wine
On Deck: Irish Red, Surly Bender clone, Spruced Warmer, CDA