Quick Definition:

Free chlorine sanitizes and oxidizes swimming pool water, keeping the water safe and clear for swimmers.

What is Free Chlorine in swimming pools?

Also called residual chlorine, free chlorine is the chlorine level in a swimming pool that performs the vast majority of sanitation duties, killing microorganisms and oxidizing organic and inorganic contaminates.  Free chlorine has no perceptible taste or smell, and does not cause any irritations, unlike combined chlorine.

The level of free chlorine in swimming pools can be determined by testing the pool chlorine level and determining the total chlorine and free values.  These two measurements can then determine any combined chlorine present in the pool water.


  • “Pool & Spa Water Chemistry, A Testing and Treatment Guide, Waterproof Edition, 2005. Taylor”

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