Preheat oven to 180 degrees C. Grease 12 muffin cups or use paper liners. Sift all-purpose flour, bicarb soda and cocoa together and set aside.
Whisk 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.