Citric acid is a weak organic acid found in citrus fruits. It is a natural preservative and is also used to add an acidic (sour) taste to foods and soft drinks. In biochemistry, it is important as an intermediate in the citric acid cycle and therefore occurs in the metabolism of almost all living things.
Because citric acid kills bacteria, mold, and mildew, it's great for general disinfecting and cleaning. It's also effective at removing soap scum, hard water stains, calcium deposits, lime, and rust. Also, it serves as a preservative in many cleaning solutions.