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Chlorine in water

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Water chlorination is one of the greatest public health discoveries of the 20th century saving many lives. Today we will take a closer look at chlorine and chlorine compounds, their advantages and disadvantages as well as find out what are the effects of chlorination byproducts on human health.

The history of chlorine

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The use of chlorine to disinfect the water is one of the scientific discoveries that changed the world.  The idea of adding calcium hypochlorite to the water came in 1984 to the chemist Moritz Traube who discovered that in this way it is possible to obtain clean water from microorganisms. In 1897, the first city to treat the water with chlorine was Maidstone (England). It stoped the typhus epidemic because  the main source of it was the water. At first water disinfection with chlorine was used in England, then in the USA but at the beginning of the 20th century this method gained popularity all over the world.

Today chlorine compounds are used to ensure the safety of drinking water.
Their main advantages are:

  • high efficiency against pathogenic microorganisms;
  • long-term effect – the ability to disinfect not only at the water treatment plant but also at pipelines during the flow preventing from repeated water contamination;
  • simple dosing in water;
  • the price of reagents is relatively lower than possible alternatives;
  • simplicity of production, the systems do not require a large amount of electricity.

Chlorination without chlorine

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Considering that the storage of liquid chlorine is dangerous, today it is replaced by safer forms of chlorine reagents. Electrolytic chlorine, chlorine dioxide, sodium and potassium hypochlorites are mainly used in centralized water supply systems. Chlorocyanuric acid salts (chlorine tablets) are suitable for decentralized systems and pools.

Sodium hypochlorite

Sodium hypochlorite (NaOCl) is the same bleach that you can buy in the stores. This reagent is produced in liquid form for both household and industrial use. This disinfectant has several advantages. The sodium hypochlorite produced by electrolysis does not emit hazardous substances into the environment, it is safe during transportation and storage, produces fewer by-products and has a less distinct smell.

Chlorine dioxide

Chlorine dioxide (ClO2) is another common reagent for water disinfection which is recognized as one of the best. It has high efficiency and does not form toxic by-products.


Chloramines are compounds of chlorine and ammonia. They are formed by adding ammonia to water treated with chlorine. This method is widely used in the USA. Chloramines form less trihalomethanes and are stable in the water. After processing less pronounced odor is observed.

Calcium hypochlorite

Calcium hypochlorite (Ca(ClO)2) was the first water disinfectant but it is not used in practice today. It forms deposits and causes certain difficulties in its application.

How does active chlorine work?

The principle of chlorine’s disinfecting effect lies in its oxidation of microbiological particles. Chlorine-containing compounds in water dissociate into perchloric acid and/or hypochlorite ions. These particles are able to emit active chlorine, destroy bacteria, viruses, fungi as well as humic and fulvic acids, phenol derivatives, quinones and other water pollutants.

How dangerous is chlorine for humans?

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In the course of water disinfection chlorination by-products/organochlorine compounds are formed. These compounds determine the effect of chlorine on the human body. In total, there are about three hundred organochlorine compounds.

The carcinogenic effects of water containing trihalomethanes have been confirmed in the last two decades.  The chlorination by-products have been actively researched for 40 years. In the course of research a certain relationship has been established between long-term drinking of water with chlorination products and bladder, colon cancer. Studies have also shown the intrauterine effects of chlorination products – a relationship between maternal consumption of chlorinated water and reduced fetal growth. Side effects such as spontaneous abortion, stillbirths and congenital defects of the nervous system have also been observed.

Despite the above it should not be forgotten that water chlorination is one of the greatest discoveries of the 20th century in the field of public health care. The risk of death from infectious diseases is much greater than the effects of organochlorine compounds.

Can water be disinfected without chlorine?

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Water can be disinfected with ozone and ultraviolet light. Dozens of reagents (hydrogen peroxide, bromine, organic disinfectants, heavy metals) and non-reagents (ultrasound, irradiation) are available for water disinfection. All these methods have certain effectiveness but at the same time they also have significant drawbacks.

For example: ozone is a strong oxidizer and can neutralize even parasites against which chlorine is ineffective but it does not have a long-term effect. Once water enters the water distribution network, it remains vulnerable from repeated microbiological contamination. For ultraviolet radiation the situation is more complicated. Its bactericidal properties are lower and applicable only to the water that has been sufficiently purified. This method is energy intensive.

Membrane technologies are increasingly being developed and used. Ultrafiltration is able to eliminate bacteria, parasites and fungal spores as well as colloidal contamination. Today it is used by many European countries as one of the stages of water treatment.

Taking care of health

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It is not a secret that the water from the centralized water supply system can be used for food and drinking only formally. The list of contaminants in tap water is quite extensive. However, there are solutions to the problem of the presence of organochlorine compounds and chlorine residues.

Filters with activated carbon can retain up to 90% of organic impurities, reverse osmosis filters can remove more than 99% of toxic substances, including trihalomethanes. High-performance carbon filter and ultraviolet disinfection system can solve the water quality problem for tap water, making it safe for consumption.

It is important to know that today’s water supply systems provide only a basic level of the water quality. The responsibility for the quality of drinking water and the health in the long term lies upon ourselves.Therefore, the water that we and our children consume today ensures the quality of our lives. Installing water purification filters and buying bottled water has now become an important part of daily care for your health.

Read also: Tap water: to drink or not to drink? , How to choose a water filter? .

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