Chloride

(endorsed 1996)

Guideline

Based on aesthetic considerations, the chloride concentration in drinking water should not exceed 250 mg/L.

No health-based guideline value is proposed for chloride.

General description

Chloride is present in natural waters from the dissolution of salt deposits, and contamination from effluent disposal.

Sodium chloride is widely used in the production of industrial chemicals such as caustic soda, chlorine, and sodium chlorite and hypochlorite. Potassium chloride is used in the production of fertilisers.

The taste threshold of chloride in water is dependent on the associated cation but is in the range 200–300 mg/L. The chloride content of water can affect corrosion of pipes and fittings. It can also affect the solubility of metal ions.

In surface water, the concentration of chloride is usually less than 100 mg/L and frequently below 10 mg/L. Groundwater can have higher concentrations, particularly if there is salt water intrusion.

Food is the major source of chloride intake. All plants and animals contain chloride. The addition of salt during processing or cooking can markedly increase the chloride content.

Typical values in Australian drinking water

In major Australian reticulated supplies chloride concentrations range up to 350 mg/L. Typical values depend to a large extent on local conditions but concentrations of 150 mg/L are not uncommon in some areas.

Treatment of drinking water

Chloride cannot be removed from drinking water by conventional water treatment processes. It can be removed by distillation or reverse osmosis but these are expensive to operate.

Measurement

The chloride concentration in drinking water can be determined with titrimetric techniques using silver nitrate or mercuric nitrate and colorimetric or potentiometric end-point detection (APHA Method 4500-Cl- Parts B or C 1992). The limit of determination is approximately 1 mg/L. Ion chromatography can also be used (APHA Method 4500-Cl- Part F 1992), with a limit of determination of 0.1 mg/L.

Health considerations

Chloride is essential for humans and animals. It contributes to the osmotic activity of body fluids. A normal 70 kg human body contains approximately 80 g of chloride.

Chloride is absorbed almost completely by the gastrointestinal tract. Healthy individuals can tolerate the intake of large quantities of chloride provided there is a corresponding intake of fresh water.

Little is known about the prolonged intake of large amounts of chloride by humans. Large salt intake has been reported to increase blood pressure but this is attributed to the sodium content rather than chloride. Similar results have been reported in studies with animals, although long-term data are not available.

No data are available on carcinogenic or genotoxic effects for chloride.

Derivation of guideline

The guideline value is based on the taste threshold in drinking water of approximately 250 mg/L.

There are no data to suggest that chloride causes health problems; hence, no guideline value based on health considerations is warranted.

References

APHA Method 4500-Cl- Part B (1992). Chloride: Argentometric method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.

APHA Method 4500-Cl- Part C (1992). Chloride: Mercuric nitrate method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.

APHA Method 4500-Cl- Part F (1992). Chloride: ion chromatography method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.