Total Dissolved Solids (TDS) are the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given colume of water, expressed in units of mg per unit volume of water, and also referred to as parts per million (ppm). TDS is directly related to the purity of water and the quality of water purification systems. HM Digital TDS Meters monitor the TDS levels from your filtration system, and will tell you when to change your RO membrane and DI resin
