Citric acid is one of the most widespread acids among plants and is found in almost all fruits, wood, mushrooms and even tobacco. Lemon juice contains 5% to 7%. It plays a central role in the metabolism of all living organisms; the human body produces about 2 g per day and breaks it down again. It is also an anti-limescale (it descales, cleans and dissolves limescale) and a fantastic anti-oxidant. Citric acid is completely biodegradable and is one of those basic household products that should be found in every home.