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. 

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.

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.

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...

• Mülheim an der Ruhr
• Oberhausen
• Bottrop
• Neuburg
• Lünen (NRW)
• Kamen, Bönen, Bergkamen

• 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.

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