Preheat the oven to 350°F (175°C) and grease the loaf pan with butter or non-stick spray.
In a large mixing bowl, whisk together the flour, granulated sugar, brown sugar, baking powder, baking soda, salt, and spices (cinnamon, nutmeg, ginger, and cloves) until well combined.
In another bowl, beat together the vegetable oil, eggs, pumpkin puree, and water until smooth.
Pour the wet ingredients into the dry ingredients and mix until just combined. Be careful not to overmix; lumps are okay.
If using, fold in the chopped walnuts or pecans.
Pour the batter into the prepared loaf pan, spreading it evenly.
Bake in the preheated oven for 60 minutes, or until a toothpick inserted in the center comes out clean.
Remove the bread from the oven and let it cool in the pan for about 10 minutes. Then transfer it to a wire rack to cool completely.