Turn Passata Into Tomato Paste? I have an American recipe that calls for 12oz Hunts Tomato paste and 1.5 cups of water.  The nearest thing I have is Passata.

I don't know much about cooking, but they both seem to be made from tomatoes...is there any way I can use the passata I have in place of the tomato paste?  I'm assuming I would reduce the water or completely skip the water - is there a general guideline here?

My instinct is to just throw it in a pot and, if it seems to watery, simmer until it thickens...but I figured I should ask people who know.
Passata is crushed tomato.  Tomato paste is a concentrate of tomato produced by cooking for a long time, removing seeds and skin, and cooking further.  They are different products that are going to produce different results, both flavor-wise and in terms of texture.  If I were you, I would not add extra water at all, if you are going to use the Passata.  I am sure it will be good...it will just be different from the intent of the recipe.