Chlorine for Water Treatment

People might sometimes get confused on what is Total chlorine, and what is Free chlorine. Here are some details that might be of help.

The chlorine that is free and available does the vital work of killing bacteria and removing contaminants. When free chlorine comes in contact with contaminants, such as soap, ammonia, or other organic compounds that contain nitrogen, it’s called combined chlorine, or as others call it: chloramines. In water of pools and spas, this type of chlorine has very little ability to sanitize, and also has no oxidizing ability. You may think of combined chlorine as a spent bullet.

Major water treatment plans often do use chloramines to provide treated drinking water.


Because combined chlorine, or chloramines, are more stable and last longer than free chlorine. Chloramines are developed specially for drinking water treatment, and they also, as a result, have very little odor.

But free chlorine has to work much harder in spas and pools due to the non-pure objects that might be found in the treated water. When free chlorine combines with contaminants such as human waste etc., the chloramines get a real bad odor.

Combined chlorine can also irritate the eyes and the skin of swimmers.

This is were shocking comes into the picture.

When the concentration of combined chlorine is more than 0.2 parts per million (ppm), one nees to shock the spa or the pool. How do you that? well, it’s sort of super chlorinating the water, and this will oxidize the combined chlorine and remove the contaminants for good.

Unfortunately, no convenient and direct testing method is available to measure the level of combined chlorine.

But, we usually start with total chlorine, which is just the sum (total!) of both: free chlorine and combined chlorine (chloramines).

  • A total chlorine test that yields a level of 5 parts per million, and a free chlorine test that yields a level of 2 ppm, indicates a combined chlorine level of 3 ppm (5 ppm total chlorine [minus] 2 ppm free chlorine [equals] 3 ppm combined chlorine).

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