FAQs – Pesticides in water

Pesticides in drinking water

Is our tap water safe to drink?

In Switzerland, tap water can be safely consumed. A report issued in September 2019 by the Swiss Association of Cantonal Chemists (available in French / German / Italian) concludes that Swiss drinking water is of good quality; regional improvements are, however, required – particularly where drinking water is sourced from groundwater in agricultural areas.

In Swiss legislation, the maximum permissible concentrations specified for organic pesticides and their metabolites (transformation products) in drinking water are very low, in accordance with the precautionary principle. This means that, in the current state of scientific knowledge, the exceedances of these limits observed in drinking water do not pose risks to human health (based on WHO toxicity guidance values).

To what extent is drinking water currently contaminated?

Swiss drinking water is sourced from ground- and lake water. These resources are, however, contaminated with pesticide residues (i.e. active ingredients and metabolites). In some cases, the limits specified in the relevant legislation (FDHA Ordinance on Drinking Water and Water in Public Baths and Shower Facilities) were found to be exceeded, e.g. for chlorothalonil metabolites.

Further information

Chlorothalonil is a fungicide formerly widely used to protect crops such as cereals, potatoes, vegetables and vines. In December 2019, all chlorothalonil metabolites were classified as relevant for drinking water by the Federal Food Safety and Veterinary Office (FSVO), since health risks cannot be excluded. Relevant metabolites in drinking water are subject to a limit of 0.1 microgram per litre (this limit is also applicable for groundwater). In 2019, a total of seven metabolites of chlorothalonil were clearly detected in groundwater; in some cases, the concentrations exceeded the currently applicable limit. Concentrations of chlorothalonil metabolites exceeding the legally specified limit were also found in drinking water.

Use of chlorothalonil has been banned since 1 January 2020.

Further information

What happens when limits for contaminants in drinking water are not met?

The following measures are implemented to ensure compliance with legally specified limits:

  • Dilution with uncontaminated water
  • Improved protection of areas of contribution
  • Installation of filtration and/or treatment systems
  • Closure of the affected groundwater well

Who is responsible for the safety of drinking water?

Responsibilities are defined as follows:

Federal authorities: Federal Food Safety and Veterinary Office FSVO and Federal Office for Agriculture FOAG – responsible for legal requirements and limits
Cantonal authorities: Cantonal Chemists – responsible for enforcement and monitoring compliance
Water suppliers: responsible for analysis and treatment of water to ensure compliance with legally specified limits for drinking water
Property owners: responsible for installations and water quality within the building

Another important organisation in the drinking water sector is the Swiss Gas and Water Industry Association SVGW, which works to ensure secure and sustainable gas and water supplies.

Who assesses the safety of pesticides and their metabolites?

The Federal Food Safety and Veterinary Office FSVO

Are the risks for humans lower than for aquatic organisms?

Yes, the risk is lower for humans because concentrations in drinking water are much lower than in streams and rivers. In addition, many pesticides are less problematic for humans because we do not spend all our lives in water. Aquatic organisms such as fish not only ingest toxicants during feeding but are also exposed via the skin and gills (respiration).

As the Swiss limit for pesticides in drinking water is set at a very low level, on a precautionary basis, Swiss tap water can be safely consumed.

Information on risks to human health is provided by the Swiss Centre for Applied Human Toxicology (SCAHT). Risks for aquatic organisms are studied by the Ecotox Centre.

Pesticides in surface waters and groundwater

To what extent are Swiss surface waters and groundwater contaminated with pesticides?

Surface waters

Numerous federal, cantonal and academic studies have shown that the concentrations of pesticides in many surface waters in agricultural areas are sufficiently high to pose risks to aquatic organisms. In 2017, for example, scientists from Eawag and the Ecotox Centre analysed water samples collected from five small streams in agricultural catchments. They concluded that risks of toxicity to sensitive aquatic organisms could not be excluded in any of the streams investigated, with exposure lasting for several months. In addition, more than 35 different active ingredients were found in half of the samples. Although the streams studied are situated in intensively used catchments, they are by no means unusual for Switzerland. It can therefore be assumed that these findings from 2017 are still relevant today. In 2019, pesticides were also detected in stream sediments.

Further information


Pesticide residues (i.e. active ingredients and metabolites) occur in groundwater at over 50 per cent of the NAQUA National Groundwater Monitoring sites across Switzerland. In intensively farmed areas, residues are detected at over 90 per cent of NAQUA sites.

Further information

What risks do the concentrations measured pose to aquatic organisms?

Ecotoxicological studies show that pesticides can adversely affect the reproduction, development and health of microorganisms, plants and animals. Pesticides thus threaten biodiversity.

Further information

Are all pesticides equally toxic to aquatic organisms?

No. Pesticides vary widely in their toxicity to aquatic organisms, as do the amounts applied. A low‑toxicity substance applied in large quantities may have the same environmental impact as a highly toxic substance used in small quantities. However, whether significant quantities of a substance can enter waterbodies will also depend on its properties; for example, it is important how rapidly a substance is degraded in soil.

The revised Waters Protection Ordinance which came into effect on 1 April 2020 takes variable toxicity into account and introduces stricter limits for pesticides of particular concern.

Further information
  • Federal Office for the Environment: media release on the adoption of stricter limits for pesticides in the revised Waters Protection Ordinance, 18 February 2020 (available in French / German / Italian)

Why can certain substances still be detected in groundwater years after their use has been banned?

Groundwater is only slowly replenished. In addition, substances take a long time to break down in low‑temperature groundwater, and there is a lack of microorganisms contributing significantly to pesticide degradation. In some cases, substances or their metabolites stored in the soil are only slowly leached into groundwater. Thus, for example, metabolites of the herbicide atrazine are still found in groundwater today, even though it has been banned in Switzerland since 2012.

Further information

Have all pesticides been covered by the studies performed to date?

No. Around 300 active ingredients for pesticides are currently authorised. Only about 50 have to be included in routine cantonal monitoring. While many cantons monitor a larger number of substances, the entire range is almost never covered. In addition, for certain substances, analytical methods have only recently been developed – e.g. for pyrethroids (potent synthetic insecticides). Moreover, the use of composite samples (usually collected over a 2-week period) means that short-term peak concentrations are hardly ever recorded.

Why do the concentrations determined in the authorisation procedure differ from the limits specified in the waters protection legislation?

In the authorisation procedure, modelling is used to assess whether a pesticide poses risks to aquatic organisms. From the risk assessment, so-called regulatory acceptable concentrations (RAC) are derived. Pesticides are only authorised if they are not expected to cause any “unacceptable adverse effects” on aquatic organisms. (Pesticides Ordinance (PSMV) Art. 1 purpose clause)

In contrast, the waters protection legislation specifies the maximum concentrations which may actually occur in the environment so that pesticides “do not detrimentally affect the reproduction, development and health of sensitive plants, animals and microorganisms” (WPO, Annex 2).

Further information

Could the contamination problem be solved by banning substances of particular concern?

Studies carried out by Eawag from 2012 to 2017 showed that, for at least 30 substances, the risks are so high that inputs to waterbodies should be markedly reduced. Whenever substances of particular concern are banned, it must be ensured in particular that this does not lead to increased use of an alternative substance creating new problems.

Under the pesticide-related measures developed for Switzerland’s agricultural policy after 2022 (AP22+), the use of substances of particular concern is to be excluded from the direct payments system or prohibited altogether.

What are Swiss policymakers doing to protect natural waters?

Particularly when groundwater (the main source of drinking water) is affected, measures are taken – e.g. the ban on chlorothalonil.

To ensure compliance with legally specified limits over the long term, the Action Plan on risk reduction and sustainable use of plant protection products was adopted by the Federal Council in 2017. Since then, numerous measures have been initiated, with the following goals:

  • reducing pesticide emissions by 25 per cent in the medium term
  • promoting alternatives to chemical plant protection
  • halving the risks currently associated with plant protection products and markedly reducing contamination with metabolites

As the active ingredients of pesticides are sometimes highly persistent and groundwater is only replenished slowly, anticipatory measures are particularly important. The effects of a ban are often only fully apparent years or decades after it has been introduced.

Other questions

How is the quality of surface waters, groundwater and drinking water currently regulated?

Water protection goals are defined in the Federal Constitution, the Waters Protection Act and Waters Protection Ordinance, the Plant Protection Products Ordinance (PSMV) and the Drinking Water Ordinance (TBDV). The most important quantitative requirements specified for pesticides are as follows:

Surface waters

  • 19 pesticides are subject to substance-specific, ecotoxicity-based limits. In surface waters used as a source of drinking water, the values specified are only applicable if they do not exceed 0.1 microgram per litre.
  • For all organic pesticides not specifically regulated, the limit of 0.1 microgram per litre is applicable.

Groundwater used as a source of drinking water

  • 0.1 microgram per litre for all organic pesticides.

Drinking water

  • 0.1 microgram per litre for each individual pesticide and relevant metabolite. Metabolites are classified as relevant if a risk to health cannot be excluded.
  • 0.5 microgram per litre for the sum of all pesticides
  • Different limits are applicable for copper (1 milligram per litre) and for aldrin, dieldrin, heptachlor and heptachlor epoxide (0.03 microgram per litre)

Detailed information can be found in the legislation mentioned above.

Further information

Where do the pesticides found in natural waters come from?

Many pesticides come from agricultural sources. According to the Agricultural Report 2016 (available in French / German / Italian), around 2200 tonnes of pesticides per year are used in Swiss agriculture. However, biocides used in urban areas also enter surface waters. In the coming decades, to further improve the situation downstream of wastewater treatment plants, CHF 1.4 bn is to be invested in additional treatment steps.

What measures are currently being implemented or are planned for the years ahead?

Plant Protection Products Action Plan

The Action Plan on risk reduction and sustainable use of plant protection products was adopted by the Federal Council in 2017. The goals of this Action Plan are to promote alternatives to chemical plant protection and to halve the risks.

Agricultural policy after 2022

Under the pesticide-related measures developed for Switzerland’s agricultural policy after 2022 (AP22+), the use of substances of particular concern is to be excluded from the direct payments system or prohibited altogether.

Popular initiatives

Two popular initiatives concerned with the protection of waterbodies and water are shortly to be voted on in Switzerland – the initiative For a synthetic pesticide-free Switzerland and the initiative For clean drinking water and healthy food – No subsidies for pesticide and prophylactic antibiotic use.

Parliamentary initiatives

A number of initiatives on the subject of pesticides have been submitted to Parliament, e.g.:

  • Parliamentary initiative of the Economic Affairs and Taxation Committee of the Council of States EATC-S (19.475): Reducing the risks of pesticide use
  • Parliamentary initiative of Beat Jans (19.430): Consistent protection of ground-, drinking, river and lake water against demonstrably harmful pesticides

How can Eawag contribute to the protection of waterbodies and water?

Research can play an important part in ensuring that the protection of water resources is increasingly in line with the objectives defined:

  • providing scientific foundations for policymakers;
  • further developing monitoring programmes;
  • developing new analytical methods in order to cover the broadest possible range of substances and also to detect extremely low concentrations of highly toxic pesticides;
  • conducting special water quality monitoring campaigns;
  • providing training and continuing education for cantonal and municipal water protection authorities.

Are there alternatives to the plant protection products widely used today?

Information on this question is available from:

Is it possible to determine the contribution of (non-synthetic) substances used in organic farming to pesticide contamination?

Active ingredients of plant protection products authorised for organic farming may also pose risks to aquatic organisms. While agents such as paraffin oil, inorganic sulphur or copper could be detected analytically, these substances also enter surface waters from other sources, or even occur naturally, so that such measurements do not generally permit conclusions about their use in organic farming.

Certain substances are not measured – for example, pyrethrum, which is related to synthetic pyrethroids, but consists of a mixture of naturally occurring pyrethrins. As a reference standard for the multiplicity of pyrethrins does not exist, only qualitative detection is possible. No such analyses have been carried out at Eawag. At present, only a small number of measurements are available for the non-synthetic insecticide spinosad. This substance was covered by the NAWA SPEZ 2017 campaign and was only detected in one sample. Overall, therefore, scant data is available. On this basis, it is not possible to assess the contribution of organic farming to pesticide contamination.