 This hydrology transport model is actually based upon the pollutant-loading metric called "Total Maximum Daily Load" (TMDL), which addresses TDS and other specific chemical pollutants.The success of this model contributed to the Agency's broadened commitment to the use of the underlying TMDL protocol in its national policy for management of many river systems in the United States.When measuring water treated with water softeners, high levels of total dissolved solids do not correlate to hard water, as water softeners do not reduce TDS; rather, they replace magnesium and calcium ions, which cause hard water, with an equal charge of sodium or potassium ions, e.g.