Preheat oven to 350°F. Grease and flour 8x4 inch loaf pan.
Cream butter, sugar, and vanilla with mixer.
Beat in egg, then add pumpkin and water. Mix until combined.
Whisk dry ingredients in separate bowl.
Add dry ingredients to wet mixture. Fold gently until just combined.
Stir in chopped walnuts.
Pour batter into prepared pan. Smooth top.
Bake 50-60 minutes until toothpick comes out clean.
Let rest in pan 10 minutes, then cool on wire rack.