Free chlorine vs total chlorine

Free chlorine and total chlorine are both measurements used in water treatment and pool maintenance to ensure water safety and cleanliness. Despite their similar names, they represent different aspects of chlorine concentrations in water and serve specific purposes in water quality management. Here is a description of the difference between free chlorine and total chlorine:

Free chlorine vs total chlorine


  • Free Chlorine: Free chlorine refers to the amount of chlorine present in active, unbound form in water. It contains chlorine which is available to clean water, disinfect it by killing bacteria, viruses and other harmful microorganisms.

  • Total Chlorine: Total chlorine includes both free chlorine and combined chlorine. Combined chlorine refers to chlorine that reacts with organic or inorganic substances in water to form chloramines. Chloramines are less effective disinfectants than free chlorine and may contribute to unpleasant odors and skin irritation.


  • Free Chlorine: Free chlorine levels are usually measured using a test kit or chlorine sensor. This measurement indicates the concentration of active chlorine available for disinfection purposes.

  • Total Chlorine: Total chlorine levels are also measured using the same methods as free chlorine but involve a different chemical reaction for both free and combined chlorine.

Ideal Level:

  • Free Chlorine: Recommended free chlorine levels in swimming pools and water systems are typically between 1.0 and 3.0 parts per million (ppm) to ensure effective disinfection while minimizing irritation to swimmers.

  • Total Chlorine: Total chlorine levels should ideally be maintained within the same range as free chlorine. However, the difference between total chlorine and free chlorine levels, known as combined chlorine, should be kept to a minimum to prevent issues such as chloramine formation and water quality degradation.

Water Quality Assessment:

  • Free Chlorine: Monitoring free chlorine levels helps assess the effectiveness of chlorine disinfection and ensure that water remains safe for use.

  • Total Chlorine: The total chlorine measurement provides insight into the overall chlorine demand of the water and helps determine the presence of chloramines, which may indicate inadequate disinfection or organic contamination.

Treatment Adjustment:

  • Free chlorine: Adjustment of free chlorine levels may include the use of chlorine-based disinfectants such as chlorine tablets, liquid chlorine, or shock treatments to maintain proper disinfection levels.

  • Total Chlorine: Monitoring total chlorine levels allows operators to adjust chlorination practices and address issues such as chloramine buildup through shock treatment or advanced filtration.

In summary, while free chlorine and total chlorine measurements are both important to ensure water safety and sanitation, they play distinct roles in water quality management. Free chlorine indicates the active disinfectant present in the water, while total chlorine includes both active chlorine and chloramines. By monitoring and maintaining proper levels of both free and total chlorine, water treatment professionals can ensure effective disinfection and maintain optimal water quality standards.