Can you add water to shortening to use in place of butter?
Shortening is all fat, while butter is fat with "other stuff":


  Commercial butter is 80–82 percent milk fat, 16–17 percent water, and 1–2 percent milk solids other than fat. Source


Therefore, shortening plus water can provide a somewhat more accurate substitute than plain shortening. Even a major shortening brand recommends adding water when substituting for butter.


  If you use shortening, but want an effect closer to butter, add 1 and 1/2 teaspoons water for every 1/4 cup of shortening. Source



To get a mixture that tastes a bit more like butter, you could use milk instead of water.
In most baking applications, the additional liquid can simply be added when other wet ingredients are mixed in.


Alternatively, combining them in advance can be done with sufficient beating, although this will incorporate air and potentially affect texture. See below a picture of shortening whipped with water for a pie crust recipe: