In a large skillet, heat olive oil over medium heat. Cook sausage, breaking into pieces, until browned (10-12 minutes).
Add spaghetti sauce and water, bring to simmer and turn heat off.
In smallish bowl, stir together ricotta, parsley, and salt and pepper.
Spread a layer of sauce in bottom of slow cooker insert. Cover with a layer of noodles (about 4) breaking them to fit and overlapping somewhat. Spread 1/3 of ricotta mixture on top. (Don’t worry too much about spreading the ricotta now, it will spread better when you add sauce). Spread 2 cups of sauce on top of ricotta. Sprinkle with about 1 cup mozzarella and 1/3 of Parmesan. Repeat layers 3 more times starting with noodles and finishing with a nice amount of mozzarella.
Cook on low in slow cooker for 4 hours.
Place slow cooker insert in oven and broil until cheese is bubbly and starting to brown. Let rest for 20 minutes and serve.