This can be complicated to understand so we’ve attempted to simplify it here in terms of what you need to understand for the purpose of safe drinking water and water filters. While chloride is a natural compound in water, chlorine on the other hand is usually added to kill microorganisms in drinking water.
Chlorine in water comes in two basic varieties: Free and Combined. Simply put
- 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.
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.
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.
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 can remove chlorine and typically removes 90% or more of the free chlorine. However, this depends on the surface time, temperature and pH. Therefore it’s a faucet filter such as TAPP is limited to about 2-3 litres of water minute.
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. Read more from WHO.
Chloride in water may be considerably increased by treatment processes in which chlorine is used. It’s also associated with corrision from piping.
Activated Carbon filters such as TAPP typically removes between 70-90% of the chloride.