Hard water can be softened by adding sodium carbonate (washing soda) or by passing the water through an ion-exchange column. Sodium carbonate, Na 2 CO 3, is also known as washing soda. It can ...
Add to a large jug or saucepan and pour over the boiling water. Then add your washing soda and washing-up liquid. Stir until dissolved and then add your essential oil or food colouring if preferred.