Perfect to make toilet fizzles: 1.5 cups bicarbonate of soda 0.5 cup citric acid 1tsp water 15drops lavender, peppermint and lemon essential oils Wear gloves. Mix the baking soda and citric acid in a small bowl. Add approximately 1 tap water and essential oils. Pack firmly into ice cube trays. Allow to dry for several hours. Remove gently and store in an airtight jar.