Total Dissolved Solids (TDS)
Water is a good solvent and picks up impurities easily. Pure water, which is tasteless, colorless, and odorless, is often called the universal solvent. Dissolved solids refer to any minerals, salts, metals, cations or anions dissolved in water. Total dissolved solids (TDS) comprise inorganic salts (principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates) and some small amounts of organic matter that are dissolved in water.
Elevated TDS levels are often due to natural environmental features such as: mineral springs, carbonate deposits, salt deposits and sea water intrusion. Other sources may include: salts used for road de-icing, anti-skid materials, sewage, drinking water treatment chemicals, storm water and agricultural runoff, and waste water discharges.
In general, the total dissolved solids concentration is the sum of the cations (positively charged ions) and anions (negatively charged ions) in the water. Therefore, the total dissolved solids test provides a qualitative measure of the amount of dissolved ions. The test does not provide us insight into the specific water quality issues, such as hardness, saltiness, or corrosiveness. Therefore, the total dissolved solids test is only used as an indicator test to determine the general quality of water.