Mix marinara sauce and water. Place a small amount of sauce in the bottom of a greased oval slow cooker. Place 3 noodles on top, breaking the outer ones in half to fit.
Sprinkle with 1 cup of cottage cheese; 2/3 cup of mozzarella and 1/3 cup of parmesan. Top with 1 ¼ cups of sauce. Repeat layers 2 more times. Top with the last cup of mozzarella cheese.
Cook on high for 3-4 hours or on low for 6-8 hours. Let stand for 15 minutes with the lid off before serving.