Brown the ground turkey in a large pot over medium-high heat, breaking it up as it cooks.
When the turkey is almost done, add the mushrooms and cook for another 1-2 minutes until the turkey is done and the mushrooms start to soften.
Mix in the marinara sauce and Italian seasoning, and then add 4 cups of water. Heat until it starts to simmer.
Add the rigatoni and continue to heat until it starts to simmer again.
Reduce the heat to medium-low so that it is gently bubbling and cook uncovered for about 25-30 minutes.