Chlorine in drinking water: limit values, risks and filtration
Free chlorine in German drinking water ranges from 0.1 to 0.3 mg/l. What the limit value means, why trihalomethanes matter and how chlorine can be filtered out.
After treatment, free chlorine in German drinking water ranges from 0.1 to 0.3 mg/l. The framework is set by the list of treatment substances under § 20 of the Trinkwasserverordnung (German Drinking Water Ordinance). The World Health Organization (WHO) specifies a guideline value of 5 mg/l, i.e. 16 times the German limit. The reason for a filter therefore lies elsewhere: in odour, taste and the trihalomethanes that form as a reaction product of chlorination.
How much chlorine is permitted in drinking water
The list of treatment substances under § 20 of the Drinking Water Ordinance permits the addition of up to 1.2 mg/l of free chlorine. After treatment, the content must be between 0.1 and 0.3 mg/l. The list is maintained by the Umweltbundesamt (German Environment Agency). The current version dates from January 2023 and was corrected in August 2024.
An explicit exception applies in the event of disruptions. Additions of up to 6 mg/l of free chlorine and residual levels of up to 0.6 mg/l are then disregarded. This applies as long as disinfection cannot be achieved otherwise or ammonium temporarily impairs it. For sodium hypochlorite, the same exception ends at 5.1 mg/l, for calcium hypochlorite at 4.7 mg/l.
| Treatment substance | Addition up to | After treatment | Exception in the event of disruption |
|---|---|---|---|
| Chlorine (Cl₂) | 1.2 mg/l | 0.1 to 0.3 mg/l | 6.0 mg/l addition |
| Sodium hypochlorite | 1.2 mg/l | 0.1 to 0.3 mg/l | 5.1 mg/l addition |
| Calcium hypochlorite | 1.2 mg/l | 0.1 to 0.3 mg/l | 4.7 mg/l addition |
| Chlorine dioxide | 0.4 mg/l | 0.05 to 0.2 mg/l | Chlorite up to 0.2 mg/l |
The World Health Organization sets the health-based guideline value for chlorine at 5 mg/l. It is derived from a tolerable daily intake of 150 µg per kilogram of body weight, based on a body weight of 60 kg and 2 litres of water a day. For an adult, this amounts to 9 mg a day.
If you drink 2 litres of water at the German maximum of 0.3 mg/l, you take in 0.6 mg of free chlorine. That is 6.7% of the tolerable amount. The WHO guideline value is therefore more than fifteen times the German upper limit.
Chloride is not the same as chlorine
Chloride is the anion of hydrochloric acid and comes from rock, road salt and wastewater. Its limit value is 250 mg/l and is listed in Annex 3 of the Drinking Water Ordinance, i.e. among the indicator parameters. Chlorine, by contrast, is a disinfectant and is added deliberately.
The difference between the two substances determines how they are assessed. The World Health Organization does not specify a health-based guideline value for chloride. The amounts found in drinking water are considered safe. From around 250 mg/l, water tastes salty and the corrosion of metals in the distribution network increases. The largest share of daily intake comes from table salt in food.
| Feature | Chlorine | Chloride |
|---|---|---|
| Role | Disinfectant, added deliberately | natural constituent of water |
| Legal basis | List under § 20 TrinkwV | Annex 3 TrinkwV, indicator parameters |
| Value | 0.1 to 0.3 mg/l after treatment | 250 mg/l limit value |
| Rationale | Hygiene in distribution | Taste and corrosion |
| By-products | Trihalomethanes | none |
Natural mineral water may contain more chloride than tap water. Annex 6 of the Mineral and Table Water Ordinance (Mineral- und Tafelwasser-Verordnung) permits the label “contains chloride” from 200 mg/l and sets no upper limit. A salty-tasting medicinal water with 800 mg/l chloride therefore remains marketable, whereas the same water from the tap would breach the indicator value. More on how the two types of water compare can be found in the article on tap water or mineral water.
In the 2022 reporting year, the federal states tested chloride in 2,371 water supply areas. Of 12,384 measurements, 5 were above the limit value, giving a compliance rate of 99.96%.
3 ways chlorine gets into tap water
3 entry pathways lead to chlorine in tap water: deliberate chlorination at the waterworks, residual amounts from network cleaning and loads from the chemical industry. The first pathway explains almost every case in the country.
- Chlorination at the waterworks. A plant doses chlorine to kill germs and keep the route through the pipe network clean. The next section shows how this works.
- Network cleaning and flushing. After a pipe burst, repair and flushing, the affected section of pipe is disinfected. For hours to days, the chlorine content there rises measurably.
- Chemical industry. More than half of the chlorine produced worldwide goes into plastics, above all polyvinyl chloride (PVC). Paper, pharmaceuticals and solvents follow. A small proportion reaches rivers and lakes via wastewater. For drinking water here, this pathway plays only a minor role.
Chlorine in drinking water is therefore the result of a deliberate step. The content stays below the limit value and can still be tasted. This is because the perception threshold is lower than the value set by law.
How a waterworks chlorinates water
2 dosing forms are common: chlorine gas from pressurised containers and sodium hypochlorite as a solution. In 2018, the Technologiezentrum Wasser (Water Technology Centre) examined more than 50 German sites. With sodium hypochlorite, the amounts added were 0.2 to 0.5 mg/l; with chlorine dioxide, 0.1 to 0.3 mg/l. The technical requirements are set out in worksheets W 229, W 296 and W 623 of the Deutscher Verein des Gas- und Wasserfaches (DVGW, German Technical and Scientific Association for Gas and Water).
In water, chlorine breaks down into hypochlorous acid and hypochlorite ions. Together, these two forms make up the free chlorine, which produces the effect. As a rule of thumb, the WHO specifies 0.5 mg/l of residual chlorine after 30 minutes of contact time at a pH value below 8.0. The dose required depends on how strongly the pH value of the water shifts the effect.
Chlorination is voluntary in Germany. The drinking water report of the Umweltbundesamt states clearly: unlike in other EU countries, the law here does not require chlorination. A supplier that protects the raw water, keeps the residence time short and maintains the pipe network can do without disinfection in line with the multi-barrier principle.
Waterworks that do disinfect are increasingly switching to chlorine dioxide or to irradiation with ultraviolet light (UV). Both methods produce 0 trihalomethanes. One side effect remains. In large cities with long pipe runs, suppliers maintain a residual concentration in summer. This ensures that even the last point of use receives clean water. That is exactly where tap water smells of a swimming pool more often than in the countryside.
Emergency chlorination and boil water notices
Emergency chlorination usually lasts 3 days to 8 weeks and follows a laboratory finding. The triggers are Escherichia coli, coliform bacteria or intestinal enterococci. For all 3, the Ordinance specifies a value of 0 per 100 ml. Any detection at all is therefore already too much.
A case from 2026 illustrates the process. On 30 March 2026, a routine sample in Rückers, part of the municipality of Flieden, detected coliform germs and intestinal enterococci. The Fulda health authority issued a boil water notice for Rückers, Leimenhof, Keutzelbuch and Krackhof. The municipality announced that the network would be chlorinated for 8 weeks. The boil water notice remained in force at the same time. In the district of Würzburg, parts of Rimpar were affected in the same year after intestinal bacteria were found.
Heavy rain is the most common trigger. Surface water pushes untreated contamination into the aquifer and, in some places, directly into the network. The germ load rises within hours. More on this can be found in the article on bacteria in tap water.
For genuine disaster situations, the Umweltbundesamt list has a separate Part III. For the Bundeswehr (German armed forces), a state of defence and major emergencies, it provides for additions of up to 260 mg/l of free chlorine from calcium or sodium hypochlorite, plus 26 mg/l from sodium dichloroisocyanurate in tablet form. Their use requires the approval of the civil protection authorities. A local boil water notice, by contrast, falls within the scope of Part I.
A boil water notice targets microorganisms, not chlorine. If you bring the water to a rolling boil for 1 minute, you kill the germs and drive off the free chlorine at the same time.
Trihalomethanes are the real reason for a filter
Trihalomethanes are reaction products of chlorine and organic substances in water; the limit value for their sum is 0.050 mg/l. Annex 2 of the Drinking Water Ordinance includes 4 compounds: trichloromethane (chloroform), bromodichloromethane, dibromochloromethane and tribromomethane (bromoform).
Germany's limit is therefore below the European value. The Drinking Water Directive of the European Union (EU) allows 100 µg/l. The German Ordinance halves this value to 50 µg/l, and has done so since 1 January 2003. If a supplier measures at the waterworks outlet instead of at the consumer's tap, a reference value of 10 µg/l applies. To avert a hazard, the health authority can temporarily permit 100 µg/l at the point of use.
| Reporting year | Supply areas | Measurements | Exceedances / compliance |
|---|---|---|---|
| 2020 | 1.845 | 7.878 | 0 100.00% |
| 2021 | 1.840 | 8.134 | 2 99.98% |
| 2022 | 1.865 | 8.193 | 1 99.99% |
The figures come from the drinking water report of the Bundesgesundheitsministerium (Federal Ministry of Health) and the Umweltbundesamt, published in 2025. Across 3 reporting years, 24,205 measurements add up to 3 exceedances.
The International Agency for Research on Cancer (IARC) lists chloroform in Volume 73 from 1999. It is classified in Group 2B, i.e. possibly carcinogenic to humans. The classification is based on animal studies; the agency rates the evidence in humans as inadequate. Bromate, a reaction product of bromine-containing raw water, has its own limit value of 0.010 mg/l.
Higher values occur in summer, when warm water, long standing times and a higher organic load coincide. A household filter is effective precisely here, because it sits at the end of the pipe and reduces free chlorine and trihalomethanes together.
What is proven about chlorine and health
Free chlorine at 0.1 to 0.3 mg/l is considered safe. The WHO guideline value of 5 mg/l is more than fifteen times higher. 2 follow-on issues are under discussion: the reaction products of chlorination and uptake via the respiratory tract when showering.
Epidemiological studies since the 1990s have linked long-term consumption of heavily chlorinated water with a slightly increased risk of bladder cancer. The evidence remains inconsistent, and the effect sizes are small compared with other risk factors. Health authorities conclude from this that the reaction products should be reduced through better treatment rather than abandoning disinfection, because otherwise the risk of infection rises.
When you shower, some of the free chlorine escapes with the steam, because hypochlorous acid is volatile. The water temperature accelerates this outgassing. For healthy adults, the amount remains small. People with sensitive airways are more likely to notice the irritant effect in an enclosed bathroom.
Pregnant women and infants.
There are indications that the reaction products of chlorination can cross the placenta, but reliable data are lacking. Reducing intake as a precaution is medically reasonable. More on this can be found in the article on tap water during pregnancy.
People with asthma and allergies.
Irritation of the mucous membranes when showering can make symptoms worse, especially in small bathrooms with poor ventilation.
People with chronic skin conditions.
Atopic dermatitis and similar conditions often react sensitively to chlorinated water.
Acute irritation occurs from 4 mg/l. A network here hardly ever reaches 4 mg/l, as that would be thirteen times the permitted residual chlorine.
Measuring chlorine in water
Measurement uses the reagent diethyl-p-phenylenediamine (DPD). The standard DIN EN ISO 7393-2 describes the method in its 2019 version; the measuring range is 0.03 to 5 mg/l. The reagent turns the sample red, and a photometer measures the colour intensity.
3 parameters need to be distinguished. Free chlorine comprises hypochlorous acid and hypochlorite, i.e. the active fraction. Combined chlorine refers to chloramines, which form from chlorine and ammonium. Total chlorine is the sum of the two.
Commercially available test strips cost a few euros and have a resolution of around 0.1 mg/l. They are sufficient for a rough check of whether the water is chlorinated. If you need reliable figures, use a photometer or ask your supplier. Every water supplier publishes a drinking water analysis for its supply area, and the chlorine value is regularly included.
A smell test is only a rough substitute for measurement. Depending on the person, the threshold lies at 0.2 to 0.5 mg/l, which is right at the level of the permitted residual chlorine. How to test other parameters is explained in the article on measuring water quality.
4 ways to remove chlorine from water
4 methods reduce the chlorine content: boiling, leaving to stand, reverse osmosis and activated carbon. 2 of them are suitable for occasional use, 2 for continuous operation. The difference shows mainly with trihalomethanes.
Boiling
Free chlorine escapes when water is heated. After 15 minutes of boiling, the content is almost completely gone. With trihalomethanes, this method only partly works, because the 4 substances vary greatly in volatility. For daily needs, the energy required is high. During a boil water notice, however, boiling is exactly the measure that counts.
Leaving to stand
Hypochlorous acid breaks down in air. In an open carafe, the chlorine content drops noticeably within 2 to 4 hours, and faster in a shallow container. The trihalomethanes remain almost entirely. Water left standing uncovered also picks up germs from the air.
Reverse osmosis
A membrane with pore sizes below 0.001 µm retains almost all dissolved substances, including chlorine, trihalomethanes and heavy metals. The price for this is wastewater, often in a ratio of 1 to 3, a higher purchase price and the loss of calcium and magnesium. If chlorine is the only concern, the technology is oversized.
Activated carbon
Activated carbon binds chlorine and its reaction products. It needs no electricity, produces no wastewater and leaves the minerals in the water. The next section explains the 3 ways it works.
| Method | Free chlorine | Trihalomethanes | Everyday practicality |
|---|---|---|---|
| Boiling | yes, after 15 minutes | partly | low, only in emergencies |
| Leaving to stand | yes, after 2 to 4 hours | low | low, risk of germs |
| Reverse osmosis | yes | yes | medium, wastewater and costs |
| Activated carbon block filter | yes | yes | high, directly at the point of use |
Activated carbon: a block filters more than granules
Activated carbon works through 3 mechanisms at the same time. Adsorption binds chlorine molecules in the porous surface, whose internal surface area is 500 to 1,500 m² per gram. Catalysis accelerates the breakdown of free chlorine into chloride, i.e. into the salt anion from the second section. Mechanical filtration retains particles and suspended solids.
Granular activated carbon is the classic design, for example in water filter jugs. The water flows past the granules and contact remains brief. Bacteria settle in the gaps. How high the risk of bacterial contamination in jug filters is depends on the replacement interval and the temperature at which the jug is kept.
An activated carbon block filter compresses the same carbon into a solid body, usually with polyethylene-based binders. The higher density forces a longer contact time, and sintered blocks achieve pore sizes of just a few micrometres. This allows the block to retain microplastics, bacteria and cysts as well. An overview of the designs can be found in the article on filtration technologies.
For everyday use, an activated carbon filter for water in block form is the best solution against chlorine. It reduces free chlorine and trihalomethanes in one step, builds up little back pressure and leaves calcium and magnesium in the water. The manufacturer specifies the replacement interval in months and in litres, and both figures apply in parallel.
What matters when choosing a filter
4 criteria determine the choice: tested filter performance, a fixed replacement interval, good flow rate and food-safe material. The first criterion separates advertising from evidence.
Tested filter performance
Two testing standards carry real weight. They come from the National Sanitation Foundation (NSF) and the American National Standards Institute (ANSI). NSF/ANSI 42 covers chlorine, taste and odour; NSF/ANSI 53 also covers trihalomethanes, heavy metals and germs. Claims without reference to a standard are unverified.
Defined replacement interval
A filter needs a specification in months and in litres. Exhausted activated carbon releases bound substances again, which is why timely replacement is part of the filter performance.
Sufficient flow rate
High-density block filters noticeably slow down the water flow. Under-sink solutions with their own spout have more reserve here than tap attachments. If you filter at the tap, also check compatibility with the aerator, because some attachments replace it.
Food-safe material.
Housings made of stainless steel or tested plastic are the standard. With materials made from renewable raw materials, it is worth taking a closer look, as the article on bioplastics shows.
The specific designs for the kitchen and household can be found in the overview of drinking water filters. For use directly at the sink, there is a separate selection of water filters for the kitchen.
Related to this topic
Alb Filter FUSION – Activated carbon against chlorine and THMs
The FUSION under-sink drinking water filter combines Active activated carbon and Nano filtration. It reliably reduces free chlorine and its by-products without changing the mineral content of the water – permanently installed, low-maintenance and without wastewater.
Frequently asked questions
Does boiling remove chlorine from water?
Yes. Free chlorine escapes as a gas when water is heated. After 15 minutes of boiling, the content is almost completely gone. The chlorine is not destroyed in the process; it passes into the air. Some of the trihalomethanes remain, because the 4 substances differ in volatility.
Can you boil and drink chlorinated water?
Yes, boiled chlorinated water is drinkable. At 100 °C, bacteria die, and free chlorine escapes at the same time. With an official boil water notice, boiling vigorously for 1 minute is the prescribed measure. For daily needs, an activated carbon filter is the more convenient option.
Is chlorine in drinking water harmful?
At 0.1 to 0.3 mg/l, free chlorine is considered safe. At 5 mg/l, the WHO guideline value is more than fifteen times higher. Acute irritation sets in at around 4 mg/l. A network here hardly ever reaches 4 mg/l.
How do you remove chlorine from tap water?
4 methods achieve this: boiling in an emergency, leaving the water to stand for 2 to 4 hours, reverse osmosis as full treatment and activated carbon for continuous use. A permanently installed activated carbon block filter reduces free chlorine and trihalomethanes in one step.
Can you filter chlorine out with a water filter?
Yes, activated carbon filters are designed for exactly this purpose. They bind free chlorine through adsorption and accelerate its breakdown into chloride. A block filter achieves higher reduction rates than granules, because the water stays in contact with the carbon for longer. The relevant testing standards are NSF/ANSI 42 and 53.
Can you smell or taste chlorine in tap water?
The threshold is 0.2 to 0.5 mg/l, which is right around the permitted residual chlorine level of 0.1 to 0.3 mg/l. The typical swimming pool smell therefore occurs even at compliant levels, especially in large cities and after emergency chlorination.
What is the difference between chlorine and chloride in water?
Chlorine is a disinfectant that is added deliberately and is present at 0.1 to 0.3 mg/l after treatment. Chloride is a natural constituent of water with a limit value of 250 mg/l. Chloride is considered an indicator parameter for taste and corrosion. Up to 250 mg/l, it is safe for health.
How much chloride is mineral water allowed to contain?
The Mineral and Table Water Ordinance sets no upper limit for chloride. Annex 6 permits the label “contains chloride” from 200 mg/l. Tap water, on the other hand, may contain only 250 mg/l, because the indicator value of the Drinking Water Ordinance applies there.
How do you measure chlorine in drinking water?
The usual method is the DPD method according to DIN EN ISO 7393-2, with a measuring range of 0.03 to 5 mg/l. Test strips have a resolution of around 0.1 mg/l and are sufficient for an initial assessment. A photometer is more accurate. The current value for your own supply area is also given in your supplier's drinking water analysis.
How long does emergency chlorination last?
3 days to 8 weeks is typical, depending on the cause and the size of the network. In Rückers in Hesse, the municipality announced a period of 8 weeks in March 2026. Information is provided via the press, public notices and local media, usually together with a boil water notice.
Is bromine in drinking water the same as chlorine?
No. Like chlorine, bromine is one of the halogens. In water treatment here, it is hardly ever used for disinfection. What matters are bromine-containing reaction products: bromoform and dibromochloromethane are among the 4 trihalomethanes, and bromate has its own limit value of 0.010 mg/l.
Are you allowed to chlorinate well water yourself?
A private water supply system is subject to the same requirements as the public supply. Only the substances on the list under § 20 of the Drinking Water Ordinance are permitted. The values of 1.2 mg/l added and 0.3 mg/l residual also apply there. The competent authority is the health authority, which monitors the system.
Sources
- Trinkwasserverordnung (German Drinking Water Ordinance) of 20 June 2023 (BGBl. 2023 I No. 159), § 20, Annex 2 Part II and Annex 3 Part I
- Umweltbundesamt (German Environment Agency): List of treatment substances and disinfection methods pursuant to § 20 TrinkwV, as of January 2023, published in the Bundesanzeiger (BAnz AT 27.01.2023 B12), corrected on 27.08.2024
- Bundesministerium für Gesundheit (Federal Ministry of Health) and Umweltbundesamt (German Environment Agency): Report on the quality of drinking water in Germany 2020 to 2022, Environment and Health series 03/2025
- World Health Organization: Guidelines for Drinking-water Quality, 4th edition, Chapter 12, Chlorine and Chloride fact sheets
- International Agency for Research on Cancer: IARC Monographs Volume 73, Chloroform, Lyon 1999
- Verordnung über natürliches Mineralwasser, Quellwasser und Tafelwasser (German Ordinance on Natural Mineral Water, Spring Water and Table Water), Annex 6
- DIN EN ISO 7393-2:2019-03, Water quality, Determination of free chlorine and total chlorine, colorimetric method
- Municipality of Flieden: Bacterial contamination in the drinking water network, notice of 30 March 2026
