Preheat your oven to 375°F and grease a 9x13-inch baking dish.
Cook the ziti according to package directions until just barely al dente (it'll keep cooking in the oven). Drain and set aside.
In a large skillet over medium-high heat, brown the Italian sausage, breaking it into crumbles as it cooks. Drain excess fat.
Stir in the marinara sauce, water, garlic powder, and Italian seasoning. Let it simmer for 5 minutes, then season with salt and pepper.
In a small bowl, mix together the ricotta, egg, parsley, 1 cup of mozzarella, and 1/4 cup of Parmesan.
Add the cooked ziti to the sausage sauce and toss to coat.
Spread half the pasta mixture into the prepared baking dish. Drop spoonfuls of the ricotta mixture over the top, then add the remaining pasta.
Sprinkle the remaining mozzarella and Parmesan evenly over the top.
Cover with foil and bake for 25 minutes. Remove the foil and bake for another 15 minutes until the top is golden and bubbly.
Let rest for 5 minutes before serving.