Free Chlorine in Water - Laboratory Analysis

The different types of chlorine

For pools and spas, there are 3 types of chlorine you can test, each with its own purpose:

•  Total chlorine - this test measures the total amount of chlorine in the water, including free chlorine and combined chlorine. It lets you check whether the total chlorine concentration is within the recommended range for effective disinfection.
•  Free chlorine - this test measures the concentration of available chlorine in the water, which is the active chlorine capable of killing bacteria, viruses, and algae. It is important to test free chlorine regularly to ensure adequate water disinfection.
•  Combined chlorine - this test measures the amount of chlorine that has bonded with contaminants in the water, forming inactive chlorinated compounds. A high combined chlorine level may indicate overchlorination or a lack of effective chlorination, which can lead to water quality problems such as skin and eye irritation.

In summary, testing total chlorine lets you monitor overall water disinfection, testing free chlorine ensures effective disinfection, and testing combined chlorine helps you detect potential overchlorination or underchlorination problems.

A closer look at free chlorine

Sources of free chlorine in water

Free chlorine or Cl2 is chlorine present as hypochlorous acid, hypochlorite ions, or dissolved elemental chlorine. It consists of active and potential chlorine and refers to all the chlorine present in the water. It represents the amount of chlorine available to combat bacteria.

Chlorination is a process that involves adding chlorine to water to decontaminate it by killing the microorganisms it contains, acting on most microbes, bacteria, viruses, and germs. However, chlorination does not completely purify water.

Standards for free chlorine in water**

According to the WHO, the free chlorine concentration in treated water should be between 0.2 and 0.5 mg/l.

Effects of free chlorine on the body

Significant exposure to free chlorine could damage the respiratory system and lungs. It may also affect the skin, particularly moist areas (armpits, groin, etc.).

Toxicity levels :

• 0.2-3.5 ppm : Odor detection threshold
• 1-3 ppm : Mild mucous membrane irritation, tolerable for a maximum of one hour
• 5 ppm : Moderate eye irritation, tearing, blepharospasm, burning sensation in the nose and throat, sneezing, coughing - Itchy skin and a burning sensation - Intolerable after a few minutes
• 14-21 ppm : Immediate throat irritation
• 30 ppm : Severe upper respiratory tract irritation - Immediate pain behind the breastbone, shortness of breath, coughing, and vomiting 
• 35-50 ppm : Fatal with 60-90 minutes of exposure 
• 40-60 ppm : Pulmonary edema that may progress to death by suffocation, pneumonia, chemical bronchitis, and lung damage 
• 430 ppm : Fatal within 30 minutes 
• 1,000 ppm : Fatal within a few minutes

* This paragraph is based in part on the WHO report “ Guidelines for Drinking-water Quality ”. 

**A guideline value is a reference value provided by the WHO.

How can you have your water's free chlorine level tested in a laboratory?

We offer laboratory analysis of your water to determine its exact free chlorine level.

To do this, you must also order the basic laboratory analysis available here. This basic analysis includes a sampling kit and shipping it to our independent partner laboratory.

Other methods for testing free chlorine in water

If you would prefer to avoid the hassle of sending samples to a laboratory, or if you expect to perform this test several times, you can test your water's free chlorine level yourself!

The eXact iDip and eXact Micro 20 photometers let you test a wide range of substances and elements in your water. Once you have the device, order the free chlorine test for photometers.