Pesticides in drinking water: limit values, origin and filters

Pesticides are the active substances in plant protection products. In agriculture and private gardens, they are applied to plants. Some of them seep into the soil and reach drinking water via the groundwater. The Trinkwasserverordnung (German Drinking Water Ordinance) limits each active substance to 0.1 µg/l and the total of all active substances to 0.5 µg/l. Exceedances are rare. Of 349 substances tested, 4 were above the limit value. An activated carbon filter binds the residues from tap water.

Plant protection products are the finished products; pesticides are their active substances. A plant protection product contains one or more active substances that protect crops from harmful organisms. In everyday language, many people use the two terms interchangeably. Technically, plant protection product means the product and pesticide the individual substance in it.

Pesticides are named after their target. Herbicides against weeds are the best-selling group. In 2024, they accounted for 32% of the 28,639 tonnes of active substances sold in Germany, followed by fungicides against fungi at 24%. Insecticides against insects hardly matter in terms of quantity but, according to the Umweltbundesamt (German Environment Agency), are highly toxic even in small amounts. There are also 4 other classes:

• Acaricides against spiders and mites
• Bactericides against bacteria
• Rodenticides against rodents
• Molluscicides against slugs and snails

Not every one of these active substances falls under plant protection law. What matters is the purpose. Anyone who uses bactericides or fungicides for disinfection rather than to protect plants is working with a biocidal product. Biocides are governed by the EU Biocidal Products Regulation 528/2012, plant protection products by EU Regulation 1107/2009.

In the reporting period from January 2017 to December 2019, 4 of 349 active substances and metabolites tested exceeded the limit value of 0.1 µg/l. This was the finding of the report by the Bundesministerium für Gesundheit (Federal Ministry of Health) and the Umweltbundesamt on drinking water quality in Germany. These 4 substances are trans-heptachlor epoxide, desethylatrazine, glyphosate and dikegulac.

Pesticides and their breakdown products (metabolites) regularly turn up in surface water and groundwater, less often in drinking water. In 2019, a quarter of all reported monitoring sites in European waters exceeded the threshold value or the environmental quality standard for at least one pesticide.

A second data set comes from the Rohwasserdatenbank Wasserversorgung, the raw water database of the DVGW-Technologiezentrum Wasser (DVGW Water Technology Centre). Between January 2010 and March 2020, 228 of 5,659 raw water abstraction points tested in Germany were above the drinking water limit value of 0.1 µg/l. For individual active substances such as bentazone, metamitron and glyphosate, the exceedance rate was at most in the low per mille range; for the metabolites, it was in the low single-digit percentage range.

The figures show 2 things. Pesticides in drinking water are not a mass phenomenon but a regional one. And the breakdown products are detected more often than the active substances themselves.

Glyphosate and desethylatrazine are among the 4 substances that exceeded the limit value of 0.1 µg/l in the 2017 to 2019 drinking water quality report. Glyphosate is a herbicide and the most widely used pesticide active substance worldwide. Desethylatrazine is the breakdown product of the herbicide atrazine.

Atrazine shows how long such substances remain in water. Atrazine has been banned in Germany since 1991 and throughout the EU since 2003. Nevertheless, the metabolite desethylatrazine still turns up in groundwater to this day. A ban takes effect quickly at the surface; in groundwater, it takes decades.

Both active substances can be reduced in tap water, but only with the right process. Glyphosate is highly soluble in water and is present in it as a dissolved molecule. Ultrafiltration forces the water through a fine membrane, such as the one used in the Alb Filter NANO cartridge. It retains particles and bacteria, whereas dissolved pesticides pass through the membrane. Activated carbon binds pesticides by adsorption on its surface and therefore remains the method of choice. With glyphosate, however, it is less effective than with other substances. The molecule is highly polar and prefers to cling to water rather than to the carbon. An activated carbon block filter lowers the glyphosate level in the water but rarely removes it completely.

The Drinking Water Ordinance limits each individual pesticide active substance to 0.1 µg/l. A limit value of 0.5 µg/l applies to the total of all active substances. The same values are set out in the Grundwasserverordnung (German Groundwater Ordinance). Relevant metabolites are subject to the same values as the active substances themselves.

The total limit value of 0.5 µg/l restricts multiple contamination, the so-called pesticide cocktail. However, it only covers the substances that are actually measured.

For metabolites, the law distinguishes 2 classes. Relevant metabolites act similarly to the parent substance and can be toxic. Non-relevant metabolites act differently from the original pesticide and are less toxic, below 50% of the active substance. The Drinking Water Ordinance sets no binding limit value for these breakdown products. There is only the guideline value of 10 µg/l from plant protection product authorisation and the Umweltbundesamt's health-related guidance value (gesundheitlicher Orientierungswert, GOW) of 1 or 3 µg/l, depending on the toxicological data available.

The Umweltbundesamt clearly criticises this gap. Of 300 known non-relevant metabolites, only 50 are monitored regularly. Such metabolites were detected at around 58% of the groundwater monitoring sites examined across Germany, some of them above the GOW.

Pesticides reach groundwater in 3 ways. The main route is application in the field. Sprayers distribute the plant protection products over the crops, and some of it penetrates the soil. There, the active substances give rise to new substances, the metabolites. Water-soluble and mobile breakdown products seep into the groundwater with the percolating water. Waterworks draw their raw water from it.

The second route is run-off. Rain washes applied pesticides from the surface into neighbouring streams and rivers. On top of this come accidents and grossly negligent use, in which large quantities reach the groundwater all at once.

Even correct use continuously introduces pesticides into the water cycle. The input is not a mishap but the rule.

According to the drinking water quality report, the levels measured in drinking water pose no risk to health. The limit value of 0.1 µg/l is far below the threshold at which a substance has a toxic effect. Greater risks arise directly during application and through contaminated food.

Pesticides are suspected of causing 4 kinds of harm in the body:

• promoting cancer
• disrupting cell division
• weakening the immune system
• interfering with the hormonal system

Article 4 of EU Plant Protection Products Regulation 1107/2009 requires proof, for authorisation, that a product does no harm to people and the environment. Nevertheless, harmful effects repeatedly come to light only years after authorisation.

For the environment, the findings are clearer. Excessive use of pesticides threatens biodiversity. Herbicides cause endangered wild plants and grasses to decline. Insecticides harm pollinators such as bees, including those that only come into contact with sprayed plants. Birds lose nesting sites and food as insect numbers decline.

An activated carbon filter removes pesticide residues from tap water. The activated carbon binds the active substances by adsorption on its porous surface. Minerals and trace elements remain in the water, because activated carbon filters selectively.

Adsorption refers to the binding of foreign substances to a surface. A single gram of activated carbon has an internal surface area of over 1,500 square metres. Plant protection product residues stick to these pore walls. The guide What is activated carbon explains in detail how this mechanism works.

Activated carbon binds more than just pesticides. It also retains chlorine, hormones, microplastics and pharmaceutical residues in tap water. The article on heavy metals in tap water provides an overview of the other pollutants in tap water.

No membrane helps against pesticides. Ultrafiltration reliably removes bacteria in tap water, but dissolved pesticide molecules are too small for that. If you want to cover both, combine activated carbon and ultrafiltration.

Activated carbon filters come in 2 designs: as loose granules and as a solid block. Loose activated carbon granules in a jug filter mainly improve taste and odour but retain pollutants only weakly. A solid activated carbon block filter achieves a higher filter performance and also binds pesticide residues.

The difference lies in contact time and density. In granules, the water seeks the shortest path between the grains. A block filter forces it through a fine, compacted carbon structure. Particularly high-quality block filters are made of sintered activated carbon. All designs are compared in the guide Activated carbon filters for water. If you are considering a jug filter, you should also be aware of the risk of germ growth in jug filters.

Alb Filter offers 2 activated carbon filters for pesticides: ACTIVE and ACTIVE+. Both work with sintered activated carbon and also bind pesticides from drinking water. The cartridges sit directly on the tap. An overview of all variants can be found under water filter cartridges.

The most effective lever against pesticides in water is less pesticide use. The EU Commission wanted to halve use by 2030 and proposed a regulation to this effect in 2022. In 2024, it withdrew the proposal after the EU Parliament rejected it. Directive 2009/128/EC continues to apply. This means there is currently no binding EU target, and responsibility remains with policymakers, agriculture and forestry, and private individuals.

At the political level, 2 points count: incentives and subsidies that support farmers in sustainable farming, and binding regulations and limit values for non-relevant metabolites. In agriculture, adapted tillage as well as retention systems and vegetated buffer strips along bodies of water reduce the input.

In private gardens, robust plants, beneficial organisms and mechanical or thermal methods against weeds are enough. When shopping, regional and seasonal food from sustainable production helps.

A drinking water filter does not solve the underlying problem. But it gives you clean drinking water straight away, while the political measures take years.