Water filters for hormones in drinking water

Since 19 January 2022, a guideline value of 1 nanogram per litre has applied to 17-beta-estradiol. It is set out in Commission Decision (EU) 2022/679. The decision placed the substance, together with nonylphenol, on the watch list. The list is based on Article 13(8) of Directive (EU) 2020/2184. Official Journal L 124 published the text on 27 April 2022.

A guideline value on the list and a limit value are two different things. A limit value is laid down in the German Drinking Water Ordinance. If it is exceeded, measures follow. A guideline value on the list initially obliges the Member States to measure. The detection limit of the analysis must be below the guideline value. For 17-beta-estradiol, this means below 1 nanogram per litre.

This leads to a point that the debate tends to overlook. Europe has only been measuring systematically since January 2023. Member States had to report their results to the Commission by 12 January 2026. A reliable body of data is therefore only just emerging.

Germany is running its own project on this. HoWiTri ran from 1 December 2022 to 1 April 2025. It was commissioned by the Bundesministerium für Gesundheit (Federal Ministry of Health). The testing was carried out by the Umweltbundesamt's drinking and bathing water hygiene department. The samples came from around 50 households. Bioassays with human cells were used. They test 4 to 6 hormonal endpoints. As of 4 August 2026, the final results were still pending.

Combined contraceptive preparations usually contain a synthetic oestrogen: ethinylestradiol. The body uses part of it. It excretes the rest in the urine. The substance remains chemically stable and largely survives conventional wastewater treatment. Estradiol and ethinylestradiol are therefore also on the list for rivers and lakes.

Then there are the body's own hormones. Every person releases oestrogens every day. This route via the bladder therefore applies to everyone, even with a completely healthy lifestyle.

According to the Umweltbundesamt (German Environment Agency), over 2,500 active substances are on the market in human medicine. For animals, there are over 400. Part of this leaves the body unchanged. Via the toilet, it ends up in wastewater. Today, 414 active substances have been detected in the environment.

This affects medicines for pain, high blood pressure and depression, as well as antibiotics. According to the Umweltbundesamt, 529 tonnes of antibiotics were dispensed in livestock farming in 2023. That is 69% less than in 2011. How such residues can be removed from water in a targeted way is shown in the article on pharmaceutical residues in tap water.

The third route is via wastewater from factories. Plasticisers, flame retardants and surfactants often affect the hormonal balance. They have persisted in the environment for decades. Nonylphenol belongs to the group of surfactants. The substance was long used as a building block for textiles and paper. Its guideline value of 300 nanograms per litre has been on the watch list since 2022. Related entries are covered in the article on heavy metals in tap water.

Professional societies and the World Health Organization name 4 types of disease. First, cancer of organs that respond to hormones. Second, metabolic diseases such as diabetes. Third, fertility disorders. Fourth, disorders in the maturation of the nervous system. How small doses act in humans remains a subject of research.

Developing life is hit hardest. Embryos, foetuses and young children are considered the group at highest risk. There, even small amounts at the wrong time are considered a risk of permanent changes.

For assessment in drinking water, the Umweltbundesamt has a dedicated tool. The health-related indicator value has 5 levels. For strongly genotoxic substances, 0.01 micrograms per litre applies. The general threshold is 0.1. For substances toxic to the immune or nervous system, it is 0.3. For substances toxic in the medium term, 1.0; in the long term, 3.0. The agency examines effects on the hormonal balance second, straight after effects on genetic material. The values only become legally binding once they are included in the Drinking Water Ordinance.

In fish, the effect is clearly proven. In polluted rivers and lakes, entire populations are becoming feminised. Ethinylestradiol, levonorgestrel and persistent industrial chemicals disrupt mating and spawning.

The burden reaches even remote locations. A team led by Joan Grimalt in Barcelona and Reinhard Lackner at the University of Innsbruck examined 9 high-mountain lakes in Spain, Poland and Slovakia. They lie at altitudes between 1,395 and 2,688 metres, far from any wastewater discharge. In the blood, liver and muscle of the fish, the team found hexachlorobenzene and polychlorinated biphenyls. Male trout had elevated levels of vitellogenin, a protein of mature females. The study was published on 25 June 2015 in Nature Scientific Reports. In this case, the input comes via the air.

Two properties make these substances a problem. First, they are biologically active even in small quantities. Second, they remain in the environment for a long time. That is precisely why waterworks, too, struggle to hold them back.

A water filter for hormones first solves a measurement problem. Detection at 1 nanogram per litre requires a laboratory. It takes equipment for chromatography combined with mass spectrometry. The limit of quantification must be below 1 nanogram per litre. For your own tap, such an analysis remains the exception.

This is exactly where the precautionary principle comes in. 3 points support it. A binding limit value is still pending. The substances are biologically active even in small quantities. And by 2033, the fourth stage will have reached only a fifth of the large plants. A filter on the tap works immediately, no matter how far along the local wastewater treatment plant is.

It makes particular sense in households with pregnant women, babies and young children. It is precisely these people that professional societies consider the most sensitive group. What else matters here is set out in the article on tap water during pregnancy.

3 methods are effective against hormonally active substances: activated carbon, reverse osmosis and distillation. A pure ion exchanger, by contrast, targets limescale and dissolved salts.

An activated carbon block filter forces the water through sintered activated carbon. The internal surface area of one gram reaches up to 1,500 square metres. Dissolved organic molecules attach to it, and hormone residues and pharmaceutical residues are precisely among them.

Three mechanisms work at the same time. Mechanically, the pore structure retains particles such as sand, rust and fibres. Catalytically, the block converts free chlorine into odourless chloride. By adsorption, it binds the dissolved organic substances, as well as lead and copper. The guide Activated carbon filters for water explains how it works in detail.

The ongoing effort is limited to changing the cartridge, roughly every 4 months depending on the model and water hardness. Which cartridge suits which purpose is shown in the overview of water filter cartridges.

Reverse osmosis forces water under pressure through a semi-permeable membrane. Its pores measure around 0.0001 micrometres. As a result, it is essentially water molecules that pass through. Dissolved substances are held back, hormones included.

The price for this is wastewater. Depending on the system, a multiple of the drinking water obtained drains away as concentrate. On top of this comes the loss of minerals. For households that put maximum purity before efficiency, the method nevertheless remains an option. The overview of filtration technologies and filtering methods puts the technical differences into context.

In distillation, water evaporates and condenses back elsewhere. Substances with a higher boiling point remain in the vessel. The end result is water of high purity.

The effort involved counts against it. Each litre takes time and energy, and the minerals are lost. The method is therefore poorly suited to the permanent supply of a household.

An ion exchanger swaps calcium and magnesium ions for sodium or hydrogen ions. This lowers the water hardness. Organic trace substances remain unaffected, because they are uncharged and escape the exchange principle.

Standard filter jugs combine an ion exchanger with loose activated carbon. The adsorption performance then depends on the quantity and contact time of the carbon, both of which are small in a jug. The design also brings a germ issue with it, which the guide on the risk of germ growth in jug filters covers with measured values.

A process from Karlsruhe reduced estradiol from 100 to 2 nanograms per litre, i.e. by 98%. It was developed by a group led by Andrea Schäfer and Roman Lyubimenko at the Karlsruhe Institute of Technology (KIT). It works photocatalytically. A large-pore membrane with palladium porphyrin generates reactive oxygen under simulated sunlight. This breaks the hormone molecules down into harmless products. The throughput is 60 to 600 litres per square metre of membrane per hour. KIT presented the work on 11 May 2021; it was published in Applied Catalysis B: Environmental.

The difference from activated carbon is fundamental. Adsorption binds the substance and holds it in the filter material until the cartridge is changed. Photocatalysis destroys the molecule. Both routes lead to clean water, but only one produces a loaded filter as residue.

The final value of 2 nanograms per litre is close to the European guideline value of 1 nanogram per litre. It will be years before such systems are in place at waterworks. For households, adsorption remains the available method.

3 limitations need to be disclosed. First, the data on German drinking water is based on a measurement obligation that has only applied since January 2023. Comprehensive evaluations of the watch list were still outstanding as of 4 August 2026.

Second, there is as yet no proven harm from the measured quantities. Nevertheless, as of 18 December 2024, the Umweltbundesamt maintains that even low concentrations in drinking water are undesirable. As its reason, it states that long-term risks are currently difficult to derive scientifically. Anyone who filters is therefore following the precautionary principle rather than reacting to proven harm.

Third, there is no recognised assessment method for mixtures of 40 individual substances in the range of a few nanograms. This is exactly where effect-based bioassays come in, such as those used in the HoWiTri project. Their results will shape assessment in the years to come. How water quality can be measured in the first place is explained in the guide How do you measure water quality.