In a large bowl combine spinach, cottage and ricotta cheese. Add salt and pepper to taste. Blend well.
Combine one cup of the spaghetti sauce and the quarter cup of water together. Spread evenly into a 13x9 inch baking dish.
Using a teaspoon, stuff each shell with equal amounts of the cheese mixture. Place stuffed manicotti into baking dish. Pour remaining cup of spaghetti sauce over the top of pasta. Cover with aluminum foil.
Bake in preheated oven for 50 minutes. Uncover and sprinkle with mozzarella cheese. Bake for an additional 10 minutes, or until cheese is melted and bubbly. Let stand 10 to 15 minutes before serving.