Citric acid is a weak organic acid that naturally occurs in a wide range of fruits and vegetables. It does not contain any anti-caking agents or fillers. Citric acid is often used as a preservative in beauty products, but more notably for making bath bombs, and for use cleaning around the home.  

Add a couple of teaspoons to your water distiller or stainless/glass kettle and boil to clean away build-up of minerals.