Chloride is the most common inorganic anion found in water and wastewater. Salt (sodium chloride) passes through the human digestive system unchanged to become the principal source of chlorides in raw sewage. The Maximum Secondary Contamination Level for drinking water for chloride is 250 mg/L.  Natural sources of salt are the ocean and various salt deposits above and below ground.

Chloride is very corrosive to most metals in systems with elevated pressures and temperatures such as boilers and oil drilling equipment. In coastal areas, higher than normal chloride concentrations in drinking water can indicate seepage of seawater into the water supply or the presence of industrial effluents.

The Titrimetric Method (Contains mercury.  Dispose according to local, state or federal laws.)
CHEMetrics employs mercuric nitrate titrant in acid solution with diphenylcarbazone as the end point indicator. Bromide and iodide will titrate as chloride. Results are expressed as ppm (mg/L) Chloride (Cl^-).

Shelf-life. Although the reagent itself is stable, the diphenylcarbazone, used as the end point indicator, has a limited shelf-life. We recommend stocking chloride test kits in quantities that will be used within 4 months.

The Colorimetric Method (Contains mercury.  Dispose according to local, state or federal laws.)
Chloride reacts with solid mercuric thiocyanate to liberate thiocyanate ion. Ferric ion reacts with thiocyanate ion to produce an orange-brown thiocyanate complex in proportion to the chloride concentration.  Results are expressed as ppm (mg/L) Cl^-.