1. Wrap sweet potato with foil and bake at 450F (230C) until tender, about 1 hour.
2. Unwrap and peel the sweet potato. Transfer to a bowl and mash. Set aside and let cool while making the batter.
3. Preheat oven to 350F (175C).
4. In a large bowl beat eggs, white sugar and brown sugar. Beat for one minute. Add oil, water and beat until combined.
5. In separate bowl stir flour, baking powder, cinnamon, salt and nutmeg.
6. Add dry ingredients to wet and mix. And mashed sweet potato and mix until well combined. Fold in walnuts.
7. Pour into loaf pan.
8. Bake for 70-80 minutes. or until toothpick inserted in center comes out clean. Let cool before serving.