Dissolved solids include any impurities that are dissolved in the water supply and comprise mainly minerals from the earth's crust. The term total dissolved solids is a measure of all impurities dissolved in a given water supply. Most dissolved mineral impurities found in water are present in the form of ions, which are electrically charged particles that are either positively or negatively charged. When dissolved in water, ions break apart in a process called disassociation. As the water temperature rises, calcium and magnesium compounds become insoluble.
Calcium carbonate is the primary source of scale in cooling and boiler water systems.
M alkalinity, or total alkalinity, is defined as the sum of carbonate, bicarbonate, and hydroxide. P alkalinity, or phenophtalein, is defined as one half of the carbonate alkalinity plus all of the hydroxide alkalinity. Carbonate and bicarbonate alkalinities can combine with calcium and magnesium hardness to form scale in cooling and boiler water systems. There are many other impurities found in natural water supplies. The most common are chloride, sulfate, iron, silica, sodium, and manganese.