Free Chlorine, Combined Chlorine, or Total Chlorine: What are the Differences?
The use of chlorine for water disinfection results in the separation of chlorine into three categories. Free chlorine, combined chlorine and total chlorine.

Free chlorine

Free chlorine is the amount of chlorine available for water disinfection. In other words, it is the number of chlorine ions that are able to attack contaminants in the water.

The importance of monitoring the amount of free chlorine in the water is justified by the fact that it is this type of chlorine that performs the disinfection. Therefore, without free chlorine in the water, treatment does not take place.

Combined chlorine

While free chlorine represents the chlorine available for water treatment, combined chlorine refers to chlorine that has already been used for disinfection, i.e. chlorine ions that have been combined with any contaminants. This means that the oxidizing capacity of this chlorine has already been used against certain contaminants.

Combined chlorine therefore occurs during water disinfection as the chlorine ions "attach" to the contaminants to deactivate them. A high concentration of combined chlorine often represents the need to add downstream treatment since it means that the concentration of organic contaminants is relatively high.

Total Chlorine

Simply put, total chlorine is the sum of the free chlorine and the combined chlorine in the water. If you know the amount of free and combined chlorine in your water, here is the formula to calculate the amount of total chlorine in your water

- Free Chlorine + Combined Chlorine = Total Chlorine.


There are many technologies for identifying chlorine, but the least expensive and therefore the most common are those that allow you to know the total amount of chlorine in the water. On the other hand, although it is relatively easy and inexpensive to identify the amount of total chlorine present in water, it is sometimes useless to know. Without information on the concentrations of free chlorine and combined chlorine, it is virtually useless to know how much total chlorine is in the water, since it is impossible to know if the chlorine present is capable of treating the contaminants in the water or if it has already been used.

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What is Water Dechlorination?
Dechlorination is an operation that removes traces of chlorine from water.