Pour 3/4 of 1 jar marinara sauce into the skillet. Add 1 1/2 cups water, 10 ounces dried penne pasta, and the remaining 1/2 teaspoon kosher salt. Stir to combine. Bring to a boil and cook, stirring frequently, until the pasta is just shy of al dente and most of the liquid has been absorbed, 8 to 9 minutes. Remove from the heat.