In a large bowl, combine ricotta, spinach, 1 C. mozzarella, ¼ C. Parmesan, egg, parsley, pepper, and onion and garlic powders. Set aside.
Stuff UNCOOKED manicotti with spinach mixture. Easiest method found to fill manicotti: put mixture in a ziploc bag, seal the bag and cut off one of the lower corners, squeeze mixture into manicotti shells.
Combine spaghetti sauce and water; spread 1 C. sauce in an ungreased 13x9-in baking dish. Arrange stuffed manicotti over sauce.
Pour remaining sauce over manicotti; sprinkle with remaining mozzarella and parmesan cheese.
Cover and refrigerate overnight (best if it sits for 24 hours and freezes well for another time). Remove from refrigerator at least 30 minutes before baking. If frozen, allow several hours or the night before to thaw.
Bake, uncovered, at 350ºF for 40-50 minutes or until hot and bubbly throughout.