I wanna make muffins using Martha White mix, and help?

Ms Nash in a box or packet mix, you can use water, but you have to be attentive, that the mix isn't overly loose. But there is a slight difference, I find with the milk added recipe, the cake seems fluffier.When water is used the cake seems more crummier, maybe it has something to do with the fat content in the milk, my wife uses my 3.25% for baking or what is known up here as full milk..