Chloride in Drinking Water Information:

Properties:

Chloride [Cl-] is a negatively charged, or anionic, species of the atom chlorine that is found in many common compounds such as sodium chloride [NaCl] (better known as table salt). It is highly soluble in water and occurs regularly in nature. It is important to note that chloride is included in the water library not because it is particularly hazardous to human health, but because it may indicate that water has been contaminated by sewage or industrial effluent. It often contibutes to a salty taste in water but is colourless and odourless. 

Sources:

Chloride in water can come from a wide variety of both anthropogenic and natural sources. Chloride is used in the production of water treatment disinfectants, coagulants, and flocculants such as sodium hypochlorite, ferric chloride, and caustic soda.1 The manufacturing of such chemicals can contribute to high chloride concentrations in raw water supplies if contaminated effluent is discharged. Run-off from roadways can also contaminate natural water sources if chloride-containing salts have been used for controlling ice and snow.2 Increases in chloride concentrations are commonly attributed to sewage leaks; sewage contains high levels of chloride along with other chemicals and bacteria that may pose a risk to human health.2

Regulations:

The limit for chloride in drinking water is 250 milligrams per litre (mg/L).

Health/Environmental Concerns:

Chloride is essential for proper functioning in the human body and is not harmful if ingested with adequate amounts of fresh water.3 However, increases in chloride concentrations can indicate that natural water sources have been contaminated by sewage. In these cases, the chemicals and bacteria present in the sewage, rather than chloride itself, are what negatively impact human health.

Action:

Chloride rarely needs to be removed from water. Instead, exceedances can be mitigated by eliminating contamination at its source. While reverse osmosis and ion exchange can be used to remove chloride, it is more efficient to control chloride levels by repairing sewage leaks or regulating the discharge of industrial effluent.1 Contact your Water Service authority if you suspect your drinking water supply has been contaminated. If drinking water makes you feel ill, contact a doctor right away.

1 Guide to the Parameters in the European Communities. What’s in your water?;  S. I. No. 278 of 2007; National Federation of Group Water Schemes: Ireland.

2 Interpretation and Standards. Parameters of Water Quality; 1-84096-015-3; Environmental Protection Agency: Ireland, 2001.

3 Guidelines for Drinking Water Quality. Aluminium in Drinking Water; Vol. 2; World Health Organisation: Switzerland, 1996.