What is the Difference Between Free Chlorine and Total Chlorine

The main difference between free chlorine and total chlorine is that free chlorine refers to chlorine in a water sample that is available to sanitize and disinfect whereas total chlorine refers to the combined concentration of both free chlorine and chloramine compounds present in a given water sample.

Chlorine, commonly used as a disinfectant in water treatment processes, plays a vital role in safeguarding public health by eliminating harmful microorganisms. Both free chlorine and total chlorine are measurements used in water treatment.

Key Areas Covered

1. What is Free Chlorine 
      – Definition, Features, Role
2. What is Total Chlorine
      – Definition, Features, Role
3. Similarities Between Free Chlorine and Total Chlorine
      – Outline of Common Features
4. Difference Between Free Chlorine and Total Chlorine
      – Comparison of Key Differences
5. FAQ: Free Chlorine and Total Chlorine
      – Frequently Asked Questions

Key Terms

Free Chlorine, Total Chlorine

Difference Between Free Chlorine and Total Chlorine - Comparison Summary

What is Free Chlorine

Free chlorine plays an important role in water treatment, serving as a powerful disinfectant that ensures the safety and cleanliness of drinking water. This compound exists in various forms, primarily as hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻), depending on the pH of the water. Its effectiveness in disinfection lies in its ability to eliminate harmful microorganisms, such as bacteria, viruses, and parasites, thereby preventing waterborne diseases.

In the water treatment process, free chlorine is often added to water as a chlorine-based disinfectant, either in the form of chlorine gas, sodium hypochlorite, or calcium hypochlorite. The presence of free chlorine in water creates an environment hostile to pathogens, as it disrupts their cell structures and metabolic processes. This ensures that the water remains safe for consumption and meets the stringent health standards set by regulatory authorities.

Compare Free Chlorine and Total Chlorine

Despite its crucial role, the use of free chlorine in water treatment raises concerns about disinfection byproducts (DBPs). When free chlorine reacts with organic and inorganic matter present in water, byproducts such as trihalomethanes (THMs) and haloacetic acids (HAAs) may form. These byproducts, though regulated, are potential health risks and have led to ongoing research into alternative disinfection methods.

What is Total Chlorine

Total chlorine is a crucial parameter in water quality assessment, reflecting the combined concentration of both free chlorine and chloramine compounds present in a given water sample. Free chlorine exists in its molecular form (Cl2) or as hypochlorous acid (HOCl) and is highly effective in disinfection. However, it can react with organic matter in water, forming disinfection byproducts (DBPs) that may pose health risks. To address this, water treatment facilities often use chloramine, a combination of chlorine and ammonia, as an alternative disinfectant. Chloramine is more stable and produces fewer DBPs.

The measurement of total chlorine provides a comprehensive understanding of the disinfection status in water. It involves assessing both the immediate disinfection potential of free chlorine and the sustained disinfection capability of chloramine. This dual evaluation is crucial for ensuring that water remains microbiologically safe throughout its distribution network.

Free Chlorine vs Total Chlorine

Monitoring total chlorine levels is essential to comply with regulatory standards and maintain water quality within acceptable limits. Excessive chlorine concentrations can result in taste and odor issues, as well as potential health concerns. On the other hand, insufficient chlorine levels may compromise the water’s ability to control microbial contaminants.

Regular testing and adjustment of total chlorine concentrations are fundamental tasks for water treatment professionals. Advanced analytical techniques, such as colorimetry and amperometry, are employed to accurately measure total chlorine levels. By maintaining a delicate balance between free chlorine and chloramine, water treatment facilities can uphold the dual objectives of effective disinfection and minimizing undesirable byproducts, ultimately ensuring the delivery of safe and potable water to consumers.

Similarities Between Free Chlorine and Total Chlorine

  • Both are measurements used in water treatment.
  • They are used for disinfection purposes in water treatment to eliminate bacteria, viruses, and other harmful microorganisms.
  • Similar testing methods, such as colorimetric or titration-based tests, are often used to quantify both free and total chlorine concentrations in water.

Difference Between Free Chlorine and Total Chlorine


Free chlorine is the active, unbound form of chlorine, while total chlorine includes both free chlorine and combined chlorine.

In Disinfection

Free chlorine is responsible for the actual disinfection of water, while combined chlorine has already reacted with impurities and is less effective at disinfection.

Form of Chlorine

While free chlorine is the chlorine available for killing bacteria and other pathogens, total chlorine includes all forms of chlorine present in the water, whether active or already combined.

FAQ: Free Chlorine and Total Chlorine

Why is it called free chlorine?

Free chlorine refers to the amount of chlorine that has yet to be combined with chlorinated water to effectively sanitize contaminants.

What is the purpose of free chlorine?

The purpose of free chlorine is to act as a disinfectant in water treatment, effectively eliminating bacteria, viruses, and other harmful microorganisms to ensure the safety of drinking water.

What is more important, free chlorine or total chlorine?

Free chlorine is often considered more important than total chlorine in water treatment, as it represents the active form available for disinfection. Monitoring free chlorine levels is important for ensuring effective water disinfection and maintaining safe drinking water quality.


1. “Free Chlorine – An Overview.” Science Direct.

Image Courtesy:

1. “Liquid chlorine” By Materialscientist –  (CC BY 3.0) via Commons Wikimedia
2. “Chlorine” By (CC BY 2.0 DEED) via Flickr

About the Author: Hasini A

Hasini is a graduate of Applied Science with a strong background in forestry, environmental science, chemistry, and management science. She is an amateur photographer with a keen interest in exploring the wonders of nature and science.

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