In a small bowl, combine enchilada sauce, mushroom soup, and onions and mix thoroughly.
Pour enough of the mix into the bottom of a 9x13 baking dish to cover the bottom. Dip each tortilla into the mix remaining in the bowl. Place a layer of the coated tortillas in baking dish. Sprinkle about 1/3 of the cheese over tortillas. Add another layer of tortillas and cheese. Add one more layer of tortillas. Pour the remaining enchilada sauce mix over the enchiladas. Sprinkle the water over the enchiladas. Sprinkle the remaining cheese on top.
Bake at 325 for 20-25 minutes or until cheese on top is melted and enchiladas are heated thoroughly.
Note: This can also be modified to make rolled enchiladas. Simply pour half the mix into the baking dish, microwave the tortillas and roll them full of cheese while warm, cover with remaining sauce mix, and sprinkle cheese on top!