Preheat oven to 350 degrees F (175 degrees C). Grease 12 muffin cups or use paper liners. Sift all-purpose flour, baking soda and cocoa together and set aside.
Whip salad dressing, white sugar, water, and vanilla together until mixed thoroughly. Add flour mixture slowly and beat at medium speed of an electric mixer for 2 minutes. Divide batter into prepared muffin pans.