The mixture is 1 cup of vinegar to 1 gallon of water. Since 1 gallon is 16 cups, it could also be 1 cup of vinegar to 16 cups of water. If we had 80 fluid ounces of water, we'd have to change the water to 5 fluid ounces to keep the mixture the same. (It's still 1 part vinegar, 16 parts water)
