How much chlorine is there in the water flowing from the tap?


The main fault that a consumer finds in drinking water is a “taste of bleach”. This is due to the use of chlorine to disinfect it. Since the bromates crisis, many Saint-Martin residents regularly complain about a chlorinated taste.

Is there really too much chlorine? To find out, we consulted the latest water quality bulletins from the regional health agency (ARS).

Chlorine is used to neutralize nonconforming materials in the water during its treatment in the plant. Then, in the network, the water always contains chlorine which is called free chlorine. It is normal for the water to still contain chlorine once it leaves the plant because it is this quantity of chlorine that will allow the pipes to be cleaned and disinfected.

A circular was issued in France in November 2003 to regulate this minimum free chlorine threshold: for supply systems using chlorine dioxide as final disinfectant - which is the case for the Galisbay plant - it is necessary "Maintain a minimum concentration of 0,15 mg / L at the outlet of the reservoirs and aim for a concentration of 0,05 mg / L at any point in the distribution network".

Overall, the level recorded by the ARS in Saint-Martin * is between 0,10 and 0,15 mg / L. At the outlet of the reservoirs, the levels recorded are rather close to the minimum threshold to have. Extracts: August 4, 2020: 0,03 mg / L, May 18: 0,17 mg / L,  May 4: between 0,05 and 0,12 mg / L (several readings), March 10, 2020: 0,16 mg / L, etc. According to the World Health Organization, the threshold for non-tolerance by consumers of the smell of chlorine in water is between 0,6 and 1 mg / L. In Australia, the odor is accepted when the content is less than 0,6 mg / L, in the United States between 0,05 to 0,1 mg / L.

Finally, the ARS raised the level of bromates several times in 2020 and it is still below 5 micrograms per liter, the threshold not to be exceeded being 10.

* On the readings available on the website of the Ministry of Health, the places where water is taken are not specified. (


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