Dr Care Digital Total Dissolved Solids (TDS) are the total weight of all Solid (minerals, salts, or metals) that are dissolved in a given volume of water, expressed in milligrams per liter (mg/L) or in parts per million (ppm). The lower the TDS level in the water, the more efficiently your body's cells actually get hydrated by the water you drink. The higher the TDS level in the water, the greater the probability of harmful contaminants that can pose health risk or hinder the absorption of water molecules on the cellular level.