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Updated on: 2020-05-14

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What has chlorine lost in drinking water?

Often the first thing you think of when you think about chlorine is your childhood: visits to the school swimming pool and the unmistakable, acrid smell that you never forget. Chlorine, an aggressive compound, was for a long time the agent of choice for water disinfection. Chlorine is a versatile chemical: in industry it is a basic material for the production of numerous organic-chemical compounds, for example chloralkanes. Chlorine gas is a deadly poison.

To protect the water, however, chlorine is added by water companies in Germany only in small quantities, which are harmless according to official standards. Even in swimming pools today, the smell of chlorine is much less than twenty or thirty years ago. Nevertheless, the topic of "chlorine in water" is still being discussed, because studies have shown that even small amounts of chlorine can have serious health hazards.

Chemical element chlorine from the periodic table with atomic number

Chlorine and chlorination of the water

The halogen chlorine is used in drinking water treatment to safely kill bacteria and other pathogens. This process is called chlorination. Depending on the pH value, it creates a balance of chlorine, hypochlorous acid and hydrochloric acid in the water. The strict regulations of the Drinking Water Ordinance (§ 11 TrinkwV) apply to the supply of chlorine to tap water. This contains a list of treatment substances and disinfection processes which is updated regularly.1

Chlorine measuring strips for testing the water

This regulation is supplemented by specifications on methodology and measures for disinfection in the rules and regulations of water suppliers, whose association DVGW has published corresponding worksheets.2 This also includes measures to prevent the formation of hazardous compounds such as trihalomethane. It is assumed that thanks to these strict standards, there is generally no danger to consumers from chlorine in tap water. This is mainly due to the low limit value of 0.3 milligrams of chlorine per liter set by the regulations for tap water in Germany. However, there are exceptional situations such as emergency chlorination and potential risks from long-term exposure, especially when by-products, so-called "disinfection byproducts", reach the consumer.

Unusual situations - how does chlorine get into the water?

Waterworks are facing new challenges, especially due to climate change. Heavy and torrential rain in particular can lead to increased germ contamination of the water. If an enormous amount of rain falls in a short time, the soil can no longer act as a natural filter. When, for example, heavy rainfall in the Bavarian Mangfall Valley in February 2012 led to water contamination, Munich's tap water was chlorinated. In Rosenheim, citizens were asked to boil the chlorinated tap water. For water companies, the faecal germ E. coli is considered a so-called "pointer germ": it must not be present in the drinking water. If it appears, measures are taken, usually chlorination. 

Boil water for at least 5 minutes during E.Coli exposure

Without water filter it is recommended to boil tap water for at least 5 minutes in case of acute contamination.

In general, whether chlorination is required regularly or only in exceptional situations depends very much on the soil conditions of a region. 80 percent of Germany's inhabitants obtain their drinking water from low-lying groundwater reservoirs that are well protected from contaminated rainwater. In Munich, people have to chlorinate about once a year when the ground is saturated by heavy rainfall. However, the situation is different in karstic regions like the Swabian and Franconian Alb.3

Chlorine is also used for bleaching and other processes in industrial processes. 40 million tons of the chemical are used every year. It is therefore also found in waste water, especially the waste water from slaughterhouses and fish processing plants. In principle, chlorine can therefore also enter drinking water through wastewater.

Dangers due to chlorine in water

Since pathogenic germs in water can pose an immediate threat to the population, the argument of using chlorine for safe disinfection always predominates in the weighing process. Despite the strictly controlled use, however, there are still discussions about the consequences chlorine can have in drinking water, even in large dilution.

In particular, by-products of disinfection with chlorine are suspected of being carcinogenic. In addition, there are voices which assume that chlorine in water poses a danger to pregnant women and unborn children. Conceivable here are the consequences of long-term poisoning if drinking water containing chlorine is consumed over long periods of time.

Greenpeace Studio says chlorine makes you sick

Although there are no absolutely reliable and generally accepted research results in this area, there are clear indications in studies and worrying findings from countries where higher chlorine concentrations in water occur. Chlorination products can also cause diseases, especially when showering and using swimming pools. Chlorine in swimming pools, for example, may cause asthma in children. The so-called THMS (trihalomethane) compounds are particularly suspected. A common THM, the well-known chloroform, could be carcinogenic. THMs are also thought to play a role in malformations and miscarriages. 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".4
Particular attention is drawn to the danger of inhaling chlorine products when taking a hot shower. In any case, very specific effects can be proven in the case of significantly increased chlorine concentrations in drinking water: An epidemiological study by Health Canada suggests that 14-16 percent of the known cases of bladder cancer in Ontario are due to an increased concentration of disinfection by-products of chlorination.5

Water filters provide remedy

Despite very strict regulations in Germany, the possibility of harmful effects of chlorine in tap water cannot be excluded. Water filters for drinking water in the kitchen and for shower and bath water can effectively prevent the possible adverse effects, especially for particularly vulnerable people.

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