The answer is that most of these veggies naturally have a lot of water that they release when we cook them. So yes! This water is enough to cook them. Since we are cooking these vegetable stir-fries in very little time, so 2-3 tablespoons of extra water are more than sufficient. Too much liquid will pull the flavor out of foods unless otherwise specified in the recipe. If using an 8 qt or a newer instant pot model that is more sensitive to burn issues, add 1/4 cup of water before pressure cooking.