Preheat oven to 350F. Grease a 9×5 loaf pan with cooking spray, or line it with parchment paper. Set aside.
Whisk together sugars, flour, spices, baking soda and salt in a large bowl. Create a well in the center of the bowl, and add pumpkin, eggs, oil, water and vanilla into the well. Whisk, starting with the wet ingredients and working your way to the outside of the bowl, mixing until batter is smooth and clump-free. Do not over-mix. (Batter will be slightly lumpy.)
Pour batter into the loaf pan, and smooth the top with a spoon. Bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean. Cool in the pan for 20 minutes, then carefully invert the loaf and cool on a rack until it reaches room temperature. Cover in plastic wrap or store in a sealed container for up to 5 days.
Notes
*If you do not have white whole wheat flour, you can just include 1 3/4 cup of all-purpose flour, instead of doing part white whole wheat and part all-purpose.Slightly adapted from AllRecipes, via The Baker Chick.