What is the difference between total, free and combined chlorine? Why do we measure free chlorine? Is chlorine and chloride the same thing? Why is chlorine added to drinking water?
The different kinds Chlorine in tap water can be complicated to understand. In this article we've attempted to simplify it in terms of what you need to understand for the purpose of safe drinking water and water filters.
Free and Combined Chlorine in tap water
Chlorine in water comes in two basic varieties: Free and Combined chlorine.
Water that is absolutely pure will only have free chlorine as there is nothing to combine with.
The amount of chlorine added depends on how much is required to destroy all organisms in the water systems. Therefore WHO, CDC, EU and other organisations recommend 0.2 to 0.5 mg/l free chlorine to remain once it's delivered to the tap as this gives a buffer. Sometimes the range is extended to 1 mg/l to ensure safety. The maximum amount of chlorine allowed is 5 mg/l. (read more). For clarity 1 mg/l can also be written as 1 ppm.
Free is the chlorine that is ready to fight bacteria and other microbes
- Combined is the chlorine that has mixed with organic matter that has mostly been used up
- Total chlorine is the combination of free and combined chlorine.
How do you remove chlorine from tap water?
Do you want to remove chlorine from tap water? When removing chlorine it's the free chlorine we want to reduce as this causes the by-products as well as potentially poor smell and taste. The combined chlorine is much more difficult to remove as it won't be adsorbed by activated carbon. Read our article about how to remove chlorine from tap water.
To measure the free chlorine in your tap you can use simple test strips. This also allows testing of tap water before and after filtering to see the results. See for example SenSafe.
Activated carbon filters such as EcoPro remove more than 90% of the free chlorine.
However the chlorine removal may differ depending on water pressure, temperature and pH. Therefore we've limited TAPP to about 4 litres of water minute.
Chloride in tap water
Chloride (Cl-1) is a natural compound in drinking water where the amount depends on the source. It's generally combined with calcium, magnesium, or sodium. Some places have less than 10mg/l while others have considerably higher amounts around 250mg/l. Sea water contains over 30,000 mg/l as NaC1. The recommended maximum allowed in tap water is 200-250mg/l. This is a
Read more from WHO.
Chloride in water may be considerably increased by treatment processes in which chlorine is used. It's also associated with leeching/corrosion from pipes.
Activated Carbon filters such as EcoPro typically removes between 50-80% of the chloride.
If you want to learn more about chlorine and chloride and how to remove them from tap water read these other blogs
Read more about how to remove chlorine and chloramine from tap water
Read more about what EcoPro removes