There are many components to a modern mains water filter system, including physical membranes, charcoal filters and ultraviolet light, but one of the most effective parts is reverse osmosis.

The concept of reverse osmosis posits that if you apply pressure to a solution to force a solvent (which in this case would be water) through a semipermeable membrane, you can separate water from the different contaminants soaked into it, making it ideal for water purification.

The reason why it is called reverse osmosis is that without the added pressure, osmosis is a process where soluble materials travel through a semipermeable membrane from a high concentrate to a low concentrate until both are equal.

It is a highly effective way to purify water, desalinate sea water for domestic use and concentrate impurities to potentially recover.

However, can it be used to filter drinking water of one of the most common contaminants in the drinking water supply of so many countries in the form of chlorine?

The short answer to this question is yes, but to understand how and why it matters, it is important to understand why chlorine gets into our drinking water at all.

Why Chlorine Matters

Untreated water is vulnerable to a wide range of contaminants and diseases that can spread rapidly and be potentially fatal.

Epidemics of diseases such as typhoid, cholera and dysentery were connected to water quality as people with worse water quality were more likely to contract waterborne diseases.

The solution, it turned out, was that by adding controlled amounts of chlorine or a chlorine compound, you can kill these diseases, and after chlorine was used to stop a typhoid epidemic in the early part of the 20th century, it has been a consistent part of water supplies ever since.

However, whilst the cheap removal of potentially fatal disease pathogens is undeniably a net positive, that does not mean that there are no issues with its application and that other forms of filtration are not more desirable.

Chlorination leaves a distinctive aftertaste and smell, which is fine to some and utterly unpalatable to others, but the bigger issue is that chlorine leaves a range of disinfection byproducts which in high doses have been linked to cancers of the liver, kidneys and bladder.

The latter is incredibly unlikely, however, so the main reason to remove chlorine from your water supply is to vastly improve the taste.

This is where reverse osmosis comes in.

Reverse Osmosis And Chlorine

Reverse osmosis removes contaminants by pushing water through a semipermeable membrane which allows water molecules through but blocks larger compounds and dissolved materials.

Typically, reverse osmosis is one of the last parts of the process, with larger pre-filters taking out silt and particles from the water supply before other processes of filtration such as activated charcoal are used.

This makes reverse osmosis very effective, removing as much as 99 per cent of chlorine molecules from the water depending on the specific filter system used, the efficiency of the membrane and other factors such as water pressure.