Sodium 

For healthy persons, the sodium content of water is relatively unimportant because the intake of sodium from other drinks and foods is so much greater. Persons following a low sodium diet because of hypertension, kidney, or cardiovascular disease should be concerned with an elevated level of sodium. The usual low sodium diet allows 20 mg/L in the drinking water. Elevated sodium levels are likely to be seen with the use of a water softener. Other possible causes are run off from road salting or sewage contamination.