I always have the correct amount of water on hand, then use a food processor and when it becomes sort of wet sand like (crumby) then I stop. Flour has different absorption levels depending on the type of flour you use, so unless they specify a certain flour, then you have to adjust the recipe. If Cook's left that out then they really suck as a teaching to cook source.
I have a grudge against them, can you tell?
Southern Lush tip: You can use white wine instead of vodka or water in a crust, mmmm. Wine.