Mix equal parts of white vinegar, water and borax. This is an easy, but effective mold-removing recipe.
Mix 1 teaspoon of borax, 3 cups of warm to hot water, 1/2 cup of white vinegar, 1 teaspoon of tea tree oil and 1/4 cup of liquid or grated castile soap, recommends the University of Arkansas Division of Agriculture. This recipe also includes other natural mold-removing ingredients such as essential oils.
Add 1/4 cup of borax to the bottle and then fill it with warm water. This solution also helps prevent mold from growing in showers and baths.