Preheat oven to 350 degrees F (175 degrees C). Have ready an un-greased 8 inch square pan.
Sift together the flour, sugar, cocoa, baking powder, baking soda and salt into an un-greased pan. Make a well in the center and pour in the water, oil, vinegar and vanilla. Mix until blended.
Bake in the preheated oven for 25 to 30 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.