Dishwasher Salt is especially designed to prevent limescale build up in your dishwasher which can cause poor performance. Finish Dishwasher Salt provides 100% better machine protection*, helping prevent limescale depositing and protecting your dishwasher by softening water when used in conjunction with the softening unit. It also helps prevent stains and watermarks accumulating on your dishes and glasses. Important: Finish Salt is specially designed for your dishwasher with 99% purity. Other salts may contain impurities that will damage the anti-cal unit of your dishwasher. *At least 2x better limescale deposit protection when using Finish Salt with Finish detergent vs using Finish detergent alone.