


Chlorine in drinking water
To protect the water (e.g. from bacteria), chlorine is only added by water companies in Germany in small quantities, which according to official standards are harmless. Swimming pools also smell far less of chlorine nowadays than they did twenty or thirty years ago. Nevertheless, the topic of "chlorine in drinking water" is a recurring topic of discussion, as studies have shown that the halogen chlorine has serious health risks - even in small quantities.
That's why we explain in this Guidebook...
- how chlorine gets into drinking water in the first place,
- what role halogen plays in drinking water treatment,
- what chlorine in drinking water has to do with heavy rainfall,
- the dangers of chlorine in water,
- what consequences inhalation in the shower can have
- and how to reliably remove chlorine from drinking water.

What is chlorine doing in drinking water?
Often the first thing that comes to mind when we think of chlorine is our childhood: visits to the swimming pool and the unmistakable, acrid smell that we never forget. Halogen chlorine, an aggressive compound, has long been the disinfectant of choice for water.
What are halogens?
The word halogen comes from the ancient Greek and means something like "salt former". In the chemical periodic table, the elements of the 7th main group are referred to as halogens. Like the other halogens, chlorine also exists as a diatomic molecule and is very reactive. Other well-known halogens include fluorine, bromine and iodine.
Use of chlorine in the chemical industry
Chlorine is a versatile chemical: in industry, it is a basic material for the production of numerous organic chemical compounds, for example chloroalkanes such as chloroform1. Chlorine gas is a deadly poison and was already used as a weapon in the First World War. Only recently, in a metal factory in Iserlohn2 released a dangerous amount of it.
As a widely used chemical in industry, chlorine often takes a detour via wastewater and thus also ends up in our drinking water. Especially in wastewater from slaughterhouses3 and meat processing plants in particular.

Good to know
In Germany, the chemical industry consumes around 40 million tons per year. If the halogen is not disposed of and is released into the environment, the degradation of the toxic chemical is very slow. This is because chlorine does not actually occur in nature in its organic form.
How does chlorine (still) get into drinking water?
When combined with water, chlorine is less harmful and is therefore used to purify tap water. The reason for this? Chlorine is comparatively cheap and can be used universally. It is therefore used by water suppliers as a disinfectant4 to kill germs, bacteria or other impurities in the water, for example.
Good to know
Good to know: Chlorine is an integral part of drinking water treatment for the purification of Tapwater .

Without a water filter, we recommend boiling Tapwater for at least 5 minutes in the event of acute contamination.
Chlorine in drinking water treatment: Chlorination
To protect the consumer , German law stipulates that water must be free from pathogens, e.g. from
- Microbes
- Viruses
- Bacteria
Halogen chlorine is used in drinking water treatment to safely kill bacteria and other pathogens. This process is called chlorination5. Depending on the pH value, it creates a balance of chlorine, hypochlorous acid and hydrochloric acid in the water.
Strict regulations?
The strict regulations of the German Drinking Water Ordinance apply to the addition of chlorine to Tapwater 6 (§ 11 TrinkwV) apply. This contains a list of treatment substances and disinfection processes, which is updated regularly.
Limit values for chlorination of water
This regulation is supplemented by specifications on methodology and measures for disinfection in the regulations of the water suppliers, whose association DVGW7 has published corresponding worksheets. These also include measures to prevent the formation of hazardous compounds such as the toxic trihalomethane8 for which there are strict limit values.
In addition, the umbrella organization for statutory accident insurance in Germany, the DGVU, also provides extensive regulations and recommendations for the chlorination of drinking water.9 are also published.
Danger from trihalomethane?
It is assumed that, thanks to these strict standards, there is generally no danger to the consumer from chlorine in Tapwater .
This is mainly due to the low limit of 0.3 milligrams of chlorine per liter set by the regulations for Tapwater10 in Germany. However, there are exceptional situations such as emergency chlorination and potential risks due to long-term exposure, especially when by-products, known as "disinfection by-products", reach the consumer.
What are "disinfection by-products"? These are disinfection by-products11that can be produced when water is chlorinated, such as the trihalomethane mentioned above.
Exception: chlorination of drinking water in emergency situations
Waterworks are facing new challenges, particularly as a result of climate change. Heavy rainfall and prolonged rainy weather in particular can lead to an increased bacterial load in the water. If an enormous amount of rain falls in a short period of time, the soil can no longer act as a natural filter.
Heavy rain as the cause
For example, when heavy rainfall led to water contamination in the Bavarian Mangfall Valley in February 2012, Munich's Tapwater was chlorinated. In Rosenheim, residents were asked to boil the chlorinated Tapwater water.
For water companies, the faecal germ E. coli is considered a so-called "indicatorgerm12": it must not be present in drinking water. If it does appear, measures are taken, usually chlorination.
Heavy rainfall in July / August 2021
After the recent heavy rainfall in July and August 2021, water had to be boiled and chlorinated in many places in Germany, for example in...
- Halingen in Menden
- Nossen near Meißen
- Bad Windsheim
- and Erftstadt (near Cologne)
Regional differences
In general, whether chlorination is required regularly or only in exceptional situations depends very much on the soil conditions in a region. 80 percent of Germany's inhabitants obtain their drinking water from low-lying reservoirs that are well protected from contaminated rainwater.
Situation in Munich
In Munich, for example, you have to chlorinate around once a year when the soil is saturated by heavy rainfall. However, the situation is different in karstic regions such as the Swabian and Franconian Jura. This is because particularly karstic soil, which is found in some places, does not have a good filter function, regardless of the amount of rainfall.
As the Süddeutsche Zeitung reports, half of German water suppliers no longer routinely add chlorine. And the head of the Federal Environment Agency's drinking water hygiene department, Ingrid Chorus, told the Münchner Tageszeitung:
"In England and the USA, people wonder how we Germans can dare to do that".13
Dangers of chlorine in water
As pathogenic germs in water can pose a direct risk to the population, the argument for using chlorine for safe disinfection always prevails in the weighing up process. Despite its strictly controlled use, however, there are always discussions about the possible consequences of chlorine in drinking water, even in large dilutions.
Research on chlorine in drinking water
Although there are no absolutely reliable and generally recognized research results, there are clear indications in studies and worrying findings from countries where higher chloride concentrations are found in water.
In addition, by-products of chlorination are also suspected of causing illness, particularly through showering and the use of swimming pools.
How chlorine benefits the swimming pool14 possibly promotes asthma15 in children. The so-called THMS (trihalomethane) compounds are particularly suspected. One common THM, the well-known chloroform, could be carcinogenic.16 be carcinogenic. THMs are also thought to play a role in deformities and miscarriages.
"Chlorine makes you ill"
The most important study on the health hazards of chlorine can be found in the Greenpeace report: "Body of Evidence: The Effects Of Chlorine On Human Health".17 The German translation "Chlorine macht krank" ("Chlorine makes you ill") reads verbatim:
"When it comes to carcinogenic chemicals, organochlorines are the absolute leaders: one third of the substances classified as carcinogenic are chlorine compounds."
Risk group: Pregnant women & mothers of infants
Pregnant women and mothers of infants in particular should exercise increased caution. There is an English study that indicates a danger for pregnant women and unborn children.18 from chlorine in water. This includes possible illnesses such as miscarriages, brain disorders, deformities and the like.
The consequences of constant poisoning over long periods of time are conceivable if drinking water laced with chlorine is consumed over a long period of time.
Beware of inhalation: danger when showering
Particular attention is drawn to the danger of inhaling chlorine products when taking hot showers. If the chlorine concentration in drinking water is significantly increased, very specific effects can be demonstrated in any case:
An epidemiological study by Health Canada19 suggests that 14-16 percent of known bladder cancer cases in Ontario are due to elevated levels of disinfection byproducts from chlorination.
How to filter chlorine from drinking water?
Despite very strict regulations in Germany, harmful effects of chlorine in Tapwater cannot be ruled out. Water filters can effectively prevent potential hazards in this respect, especially for particularly vulnerable people.
In principle, activated carbon block filters as well as ion exchangers and filters that work with reverse osmosis are suitable for filtering chlorine out of the water. Questions such as these play a role in choosing the right filter:
- Where should the water filter be used?
- What demands are made on the performance of the water filter?
You can find out more about this in another article: Filtering chlorine from water.

FAQs
Does Tapwater contain chlorine?
The legal limit for chlorine in drinking water is 0.3 milligrams per liter (Drinking Water Ordinance). Chlorine in water is intended to kill bacteria, germs and other impurities in the water and guarantee the quality of the drinking water.
What happens if you drink too much chlorinated water?
As long as the water does not contain any germs or bacteria, it is no big deal if you choke while swimming and drink chlorinated swimming pool water. However, if the water gets into your windpipe when you swallow it, this can have consequences for your lungs or bronchial tubes.
Is chlorine harmful to the body?
Chlorine in itself is not dangerous to the human body. However, there are many chlorine compounds that are extremely toxic, such as chlorine gas. There are also a number of studies that indicate that the by-products of water chlorination in particular can be extremely harmful to the body.
How do I get chlorine out of the Tapwater?
In principle, activated carbon block filters are very suitable for filtering chlorine from water. Thanks to the porous, fine-pored surface, this type of filter has a strong catalytic and adsorptive effect and can remove 99.99% of chlorine and chlorine compounds from the water.
Is chlorine in water destroyed during boiling?
Chlorine is a fairly volatile substance that evaporates when water is heated. If you boil water to eliminate chlorine or other harmful substances such as bacteria, the water should boil for at least 5 minutes.
Related articles and products
References
- https://de.wikipedia.org/wiki/Chloroform
- https://www.zeit.de/news/2021-08/13/chlorgas-in-industriebetrieb-zehn-mitarbeiter-verletzt
- https://www.prevor.com/de/chemische-risiken-in-der-fleischindustrie/
- https://www.umweltbundesamt.de/sites/default/files/medien/3521/dokumente/200114_21._bekanntmachung_der_liste_der_aufbereitungsstoffe_und_desinfektionsverfahren_gemaess_ss_11_der_trinkwasserverordnung_0.pdf
- https://en.wikipedia.org/wiki/Water_chlorination
- https://www.ris.bka.gv.at/GeltendeFassung.wxe?Abfrage=Bundesnormen&Gesetzesnummer=20001483
- https://www.dvgw.de/themen/wasser/wasserqualitaet/desinfektion/
- https://en.wikipedia.org/wiki/Trihalomethane
- https://publikationen.dguv.de/widgets/pdf/download/article/3153
- https://www.umweltbundesamt.de/themen/wasser/trinkwasser/rechtliche-grundlagen-empfehlungen-regelwerk
- https://www.lenntech.de/desinfektionsnebenprodukte.htm
- https://www.sueddeutsche.de/gesundheit/chlor-im-trinkwasser-mit-chemie-gegen-den-dreck-1.1121889
- https://www.sueddeutsche.de/gesundheit/chlor-im-trinkwasser-mit-chemie-gegen-den-dreck-1.1121889
- https://www.researchgate.net/publication/222136311_Swimming_pool_chlorination_A_health_hazard
- https://pubmed.ncbi.nlm.nih.gov/8775165/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3229674/
- https://www.oekorecherche.de/sites/default/files/publikationen/vollchlor.pdf
- http://sciencev1.orf.at/science/news/48785
- https://www.canada.ca/en/health-canada/services/publications/healthy-living/guidelines-canadian-drinking-water-quality-trihalomethanes/page-11-guidelines-canadian-drinking-water-quality-trihalomethanes.html