The Environmental Protection Agency establishes a recommended range of TDS in drinking water at 500 parts per million or lower. The total dissolved solids represent the accumulated content of organic and inorganic substances contained in water.
The organic and inorganic substances included in the TDS calculation include ionized, micro-granular and molecular substances suspended in water. The average TDS level in U.S. municipal water supplies is 350 ppm. The TDS level in municipal water resources potentially fluctuates fairly rapidly. The World Health Organization reports that some scientists and health specialists maintain that the maximum TDS level should not exceed 50 ppm.