Chlorine is one of the most commonly used agents for disinfecting drinking water. Its primary task is to eliminate bacteria, viruses, and other microorganisms that can pose a threat to human health. Thanks to chlorination, water becomes safe for consumption and does not require additional sterilization before use. However, despite its advantages, chlorine can also have an adverse effect on water installations and hydraulic equipment.
The first documented use of chlorine for disinfecting drinking water took place at the beginning of the 20th century – precisely in 1908 in the USA. At that time, engineers John L. Leal and George Warren Fuller implemented a system of continuous water chlorination in the municipal waterworks in Jersey, which significantly reduced the incidence of infectious diseases such as typhoid fever and cholera.
After this success, the method quickly spread to other cities in the United States, and then to the whole world. In Europe, chlorination began to be used around 1910, even before World War I, including in Great Britain and France - although the outbreak of World War I significantly slowed the dissemination of chlorination, as most public funds were obviously spent on army needs.
Since that time, chlorination has become the most common method of disinfecting drinking water worldwide. Chlorination enabled the elimination of many infectious diseases - as many bacteria were transmitted through water. It also significantly reduced child mortality (children are particularly susceptible to infections, e.g., due to the presence of E. Coli or Legionella in water).
Currently, despite the development of modern technologies such as ozonation or UV disinfection, chlorine remains the standard and mandatory disinfectant in most water supply systems – especially where it is necessary to maintain continuous microbiological protection of water during transport to the user. Without chlorine, Western civilization would not have achieved its current life expectancy - even if opinions or trends towards returning to a life in harmony with nature are increasingly emerging.
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Chlorine used in gaseous, liquid (e.g., sodium hypochlorite) or solid (chlorine tablets) form acts as a strong oxidant. It destroys the cellular structures of microorganisms, ensuring effective water disinfection. Furthermore, its action is long-lasting – unlike other disinfection methods (e.g., ozonation), chlorine retains its properties in the water supply network, protecting the water all the way to the point of use.
Chlorine is used not only in water supply networks but also in swimming pools. The lack of its use would essentially force such facilities to bear enormous costs of water replacement.
Chlorine, despite its bactericidal effectiveness, can affect the physicochemical properties of water. In excessive concentrations, it causes:
For this reason, the amount of chlorine in drinking water is strictly controlled and maintained at a level that ensures user safety with minimal impact on water quality. This is strictly regulated by national legislation and the EU directive on water quality - which obliges individual EU countries both to care for water purity and to ensure safety by not exceeding safe doses of chlorine.
Chlorine, as a strong oxidant, can accelerate corrosion processes in metal components of installations. This applies especially to steel, brass, and copper pipes, but also to fittings, valves, tanks, or heat exchangers. Over a long period of operation - if chlorine concentrations are high - this can lead to:
Particularly sensitive are devices such as:
To reduce the negative impact of chlorine on water systems, various solutions are used:
☑️✅ However, it must be remembered that under normal conditions, water should not have increased chlorine content - the water supplier is responsible for this. Therefore, special attention should be paid to this only in the case of special conditions or exceptional situations.
For example, in the case of having a swimming pool where chlorine will be used in higher concentrations (which is almost certain) the components of the heating or filtration system must be chosen carefully. This applies in particular to filters and heat exchangers - the latter must be dedicated to pools, not classic heating systems.
In the case of pools or well water, the use of chlorine can be partially limited - for example, by using bactericidal UV sterilizers.
In pool technology, there are also special chlorine generators using salt (so-called salt electrolyzers). These are devices that produce chlorine directly on-site through the process of electrolysis of a common salt solution (sodium chloride – NaCl). Less frequently - but still - they are also used in larger heating systems in industrial buildings. It is worth remembering that these solutions are particularly risky - for individual heating components, as salt residues can be very harmful. High concentrations of chlorine combined with salt will, over time, break down even higher-quality stainless steel.
Simply put, salt dissolves in water, and then in an electrolytic chamber, under the influence of electric current, a chemical reaction occurs:
As a result of this reaction, chlorine (Cl₂) is produced, which serves to disinfect the water, and sodium hydroxide (NaOH), which slightly raises the water's pH.
Chlorine remains an indispensable element in the process of treating and disinfecting drinking water, ensuring sanitary safety. However, its presence in water installations can lead to accelerated wear of hydraulic components, corrosion, and deterioration of utility water quality - but this should be approached rationally and the threat should not be demonized, unless it concerns exceptional situations. Therefore, it is recommended to use solutions that limit its harmful effects, such as carbon filters and chemically resistant materials - when there is an indication for it.
Properly balancing the chlorine level in water allows for a compromise between microbiological safety and the durability of hydraulic systems – which is crucial both for individual users and for large water installations in residential or industrial buildings.
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