Total Dissolved Solids (TDS) refers to the ions and other particles dissolved in the water that you can't see. Be careful not to confuse this test with conductivity, which measures the electrical conductance of water. The two are closely related, but no the same. The major components of TDS are bicarbonate, calcium, sulfate, hydrogen, silica, chlorine, magnesium, sodium, potassium, nitrogen, and phosphorus. It is essential to maintain a constant level of these solids. For example, a sudden increase is salt from brine leakage of a mineral extraction pond can have a devastating effect on the aquatic life. Streams containing flow primarily from groundwater have a high TDS level as minerals leach into the water as it filters through the rocks. Storm water is usually low in TDS.