Easy Crumb Rhubarb Pie

1 cup all-purpose flour 1/4 teaspoon salt 1 cup rolled oats 1/2 cup white sugar 1/3 cup shortening, melted 3 cups diced rhubarb 1/2 cup white sugar 1/4 teaspoon ground cinnamon 1 tablespoon water 1 tablespoon butter   Preheat oven to 350 degrees F (175…