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Like any natural product water is not free of trace substances. Precisely because we value water as a natural product, it doesn't make sense to insist on its purity. The fact that tap water in Switzerland is nevertheless of outstanding quality and can be drunk without hesitation is the provisional result of a long-development.


Tap water is the most controlled foodstuff in Switzerland and meets the highest standards of hygiene and safety. It is extremely healthy, supplies us with minerals, quenches thirst and increases concentration. Around 2500 water suppliers ensure this every day in Switzerland. 99.9% of drinking water consists of water. The rest is composed of minerals, salts and trace substances in minute quantities. A list of all Swiss bodies of water, their composition and information on individual ingredients can be found here.

Example of Spring Water in Lucerne:

Total hardness: 14.7 fH°

pH value: 8.1

Calcium: 53 mg/l

Magnesium: 3.7 mg/l

Potassium: 1 mg/l

Chloride: 1.1 mg/l

Nitrate: 3.6 mg/l

Sulphate: 9.6 mg/l


Pesticides in drinking water: How should the findings on chlorothalonil be assessed?

A reassessment in summer 2019 classified degradation substances of chlorothalonil as health relevant for the first time. As a result, they must now comply with the official limit value for Swiss drinking water. Swiss water utilities are responding to the situation by quickly and efficiently adapting affected drinking water wells through numerous controls. That is why tap water can still be drunk without hesitation.


Drinking water is obtained in various ways. According to the geographical location, one way usually makes more sense than others.

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In Switzerland, about 40% of drinking water is spring water. This water is mainly found in the Alps and the Jura. Spring water undergoes various natural purification processes. In the mountains, the water flows over gravel and stones and slowly seeps through various layers of soil into the subsoil. The water is thereby purified and absorbs valuable minerals such as magnesium or calcium carbonate.

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Another 40% of drinking water comes from groundwater. Groundwater resources in Switzerland amount to over 50 billion cubic metres of water - roughly equivalent to the volume of water in Lake Constance. We find it mainly in the Swiss midlands. Groundwater seeps deep into the soil layers and absorbs a corresponding amount of minerals, which influences the intensity of the taste.

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The remaining 20% is obtained from 30 lake waterworks. In lake basins, water from various tributaries is stored for a long time and is therefore very soft. As it is exposed to the influences of civilisation in the city and its surroundings, it is treated in several stages.

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Treatment of Spring Water

Shortly before leaving the ground, the spring is captured with drainage pipes (1). It then flows via a settling basin (2) into a reservoir (3) and from there into the supply system (4). Spring water has several advantages. Firstly, it usually does not contain any micropollutants and secondly, the difference in height between the reservoir and the households naturally creates sufficient pressure, which is why only very few electricity is needed to process and distribute it. This makes spring water the most ecological and cheapest way of obtaining water.

Groundwater Treatment

To extract groundwater, a shaft with small crevices is constructed (1). The water flows through this shaft, is pumped into the reservoir (2) and fed into the supply system (3). In the case of groundwater, preventive treatment with UV sterilisation is usually sufficient. Besides the natural cleaning processes during infiltration, this is made possible through groundwater protection. This protection clearly regulates agricultural and industrial activities surrounding a groundwater plant. Nevertheless, new trace substances call for intensified protection.

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Treatment of Lake Water

Thanks to strict guidelines for water protection, lake water is very clean even without treatment and would usually already be safe to drink. However, equally strict guidelines for drinking water require additional treatment in order to minimise even the smallest residues. Ozonation kills germs and bacteria preventively (1), quartz sand filter out larger particles (2), activated carbon breaks down biologically active substances (3) and chlorine dioxide prevents the formation of microbes in the network (4). From there the water reaches a reservoir (5) and the supply network (6). The treatment can be further optimised with the latest ion filters. These processes are relatively energy intensive, but the enormous volume of the lakes compensates for the costly treatment and makes it an attractive source.

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Measuring Techniques

Analytical instruments were further refined over the past decades. Today they can identify substances down to the nanogram. It is for example possible to detect a single sugar cube dissolved in Lake Constance. This is why people today know much more about the composition of water and are discovering new trace substances. However, this does not mean that the quality of water is deteriorating. On the contrary: we can take the necessary measures to combat undesirable substances precisely because we know more and more about water. This is why the quality of water is getting better and better.

More and more trace substances have been detected in water in recent years. However, this is not because the water quality is deteriorating, but because modern analytical instruments are becoming more and more accurate. It is one of the reasons why the quality of water has become better and better.

Trace substances in surface water have negative effects on animals and microorganisms. For humans, however, there is no health risk whatsoever, be it when bathing or drinking water. The quantities are far too small for this.

Trace Substances

Trace substances are foreign substances that are released into water by humans. These include pesticides, industrial and household chemicals, plasticizers and substances from personal care products. Trace substances are detectable in surface water and partly in ground and drinking water. They can pollute ecosystems and cause serious damage to fish or microorganisms such as crayfish in small streams or rivers in particular. It is therefore important to take measures to protect our waters effectively and sustainably. The concentrations in surface water are already very low, however, and pose no health risk for humans. They are even lower in drinking water and tap water is therefore safe to drink in any case.

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How big are Micro and Nanograms?

Trace substances are found in water in the form of micro and nanograms. At a first glance, this may look like a lot. The following example shows how to classify this almost unimaginably small unit of measurement: If you drink water with a concentration of 100 ng/l of the drug aspirin, a daily consumption of two litres would take 700 years to absorb the dose of a single aspirin tablet.


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The development of a society or culture is closely linked to the way it deals with water. Until well into modern times there were hardly any household water connections. The vast majority of the population obtained drinking, washing and cooking water from wells. It was not until the last third of the 19th century that the larger Swiss cities began to set up central water supplies (Bern and Zurich in 1868, Lucerne in 1873). The main reason for the modernisation was the protection of the cities from fire because the houses were built with wood and close together.

The use of the new infrastructure overstrained the authorities, however, and the new distribution system led to widespread cholera or typhoid epidemics due to inadequate water treatment.

At the turn of the century, water was discovered as an infection route for the transmission of cholera (1883) and typhoid fever (1906) and it was recognised that a poorly maintained tap water system spreads the dangerous pathogens. The health and hygiene of the population then became a driving force for innovation. The organisational structure of the water system in particular led to political discussions.

Especially among private suppliers problems such as unequal distribution and poor quality arose. Due to this the larger cities gradually opted for public or public-private schemes. Towards the end of the 20th century, the entire population was supplied with safe drinking water through continuously enhanced infrastructure and the tapping of lake water. Cholera and typhoid fever disappeared from Switzerland. The focus increasingly shifted in the direction of wastewater management and the associated protection of bodies of water and groundwater.

Around 1900, the infection routes for the transmission of cholera and typhoid fever through water were discovered. This shifted the driving force of innovation for a systematic water supply from fire protection to the health and hygiene of the population.

Groundwater Protection & Wastewater Management

Increasing industrialisation (polluted wastewater), new applications in agriculture (fertilizers, pesticides) and new products for personal hygiene and clothes (e.g. detergents) are polluting Switzerland's waters with trace substances. Particularly in cities open cesspools sometimes occur. The national government passed a law on the protection of fish stocks on the initiative of the fishing association as early as the end of the 19th century.

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Further measures, however, have little effect at first. Pollution due to foreign substances can have a negative impact on groundwater, one of Switzerland's most important water resources. It was only gradually that groundwater protection zones were enshrined by law and maximum numerical values were set for the input of wastewater and fertilisers into the environment and bodies of water.

Groundwater is one of the most important water resources in Switzerland. At the same time it is very sensitive. Due to very slow water flows, pollution can persist for decades.

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Bathing prohibited!

Until the 1980s, foamy streams, rivers and lakes due to high levels of pollution were part of everyday life in Switzerland. Bathing in open waters was sometimes forbidden or only permitted at one's own risk. This was particularly the case as wastewater was discharged into surface waters without any treatment. This situation became intolerable due to the population growth and measures were introduced step by step.

The "Generationenwerk Abwasserreinigung" was launched in the middle of the 20th century: the systematic construction of wastewater treatment plants (ARA), co-financed by the federal government. Between 1971 and 1990 alone, the percentage of households connected to ARA increased from 30% to 90%. All these measures had an effect: bathing in surface waters is possible basically all throughout Switzerland, and the input of trace substances has been sustainably reduced.

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Although the situation has been improved considerably in recent decades, further water protection measures are needed. These include, in particular, improved ARA for filtering new trace substances and a reduction in pesticide discharges from agriculture.

Nevertheless, there is a need for action especially in two major areas. Firstly, action must be taken against micropollutants stemming from densely populated areas. To this end, ARAs are currently being upgraded to filter out most trace substances before they are released into the environment. Secondly, further reductions in pesticide and fertilizer residues discharged into rivers and streams are needed.

In order to prevent small and medium-sized streams and rivers from becoming heavily polluted, great efforts are needed in agriculture. Due to this, a federal action plan for risk reduction and the sustainable use of plant pesticides has been drawn up. This action plan sets out various measures, but is also criticised for setting too low a target. Further actors are therefore called upon to protect groundwater and thus drinking water. This is because groundwater as an extremely sensitive drinking water resource only recovers very slowly from any contamination. The BAFU provides information on the current status, risks and measures with regard to water quality here.