Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9 inch round pan. Sift together flour, ginger, cinnamon, baking powder, baking soda and salt. Set aside.
In a large bowl, cream butter and brown sugar until light and fluffy. Beat in the egg and molasses. Add flour mixture and water. Beat until smooth.
Pour batter into pan. Bake at 350 degrees F (175 degrees C) for 30 to 35 minutes, or until a toothpick inserted into cake comes out clean. Cool in pan on a wire rack for 10 minutes. Remove from pan and serve warm.