Combine marinara sauce and water in medium bowl. Combine ricotta cheese, 1 1/2 cups of mozzarella cheese, spinach, eggs, parmesan cheeses and pepper in a separate medium bowl.
Pour one-quarter of sauce mixture onto bottom of 6-quart slow cooker sprayed with nonstick cooking spray. Top with 4 lasagna noodles, broken to fill and overlapping as needed. Spread one-third of cheese mixture over noodles. Repeat layers of sauce, noodles, and cheese mixture 2 more times. Top with remaining sauce and remaining 1/2 cup mozzarella cheese.
Cover: cook on low for 3 to 4 hours or until noodles are tender. Turn slow cooker off. Keep covered; let sit for 30 minutes.