Pesticides in drinking water — Explainer video

Transcript

Pesticides in drinking water: what chlorothalonil means for Switzerland.

Just over 80 per cent of Swiss drinking water comes from groundwater. NAQUA, the National Groundwater Monitoring, keeps watch over it at more than 600 sites.

The fungicide chlorothalonil was widely used from the 1970s onwards. In 2019, measurements showed its breakdown products to be widespread in groundwater and drinking water. In December 2019 the federal authorities withdrew its authorisation with immediate effect. Values above 0.1 micrograms per litre occur in the groundwater of 16 cantons.

The breakdown products have remained. They form in the soil when active substances decompose, seep into the groundwater with the rain and are extremely persistent. Concentrations are falling, but at many abstraction points it is likely to take years to decades before the values drop significantly.

According to a federal estimate, between 2019 and 2021 around a tenth of the population drank water with these breakdown products above the maximum level. Those mainly affected are municipalities on the Swiss Plateau. For just under 300 water supply systems, measures have been ordered.

The authorities stress that the maximum level of 0.1 micrograms per litre is a precautionary value. In their assessment, there is no short-term health risk, and tap water can still be drunk. Water utilities must nevertheless remedy exceedances. In addition, whether the maximum level applies to all these breakdown products is an open legal question.

Water utilities turn to simple measures first: taking contaminated abstraction points out of service, blending contaminated water with uncontaminated water or obtaining water from neighbouring supply systems. The Federal Council regards technical treatment as a last resort.

Natural mineral water is subject to different rules from tap water. Pesticides and their breakdown products must not be present in it at all, nor may they be removed. What a water utility is allowed to achieve with activated carbon or membranes, the catchment area has to deliver for a mineral spring.

The water of Piz Sardona seeps into the ground at more than 2,000 metres above sea level, in an area without arable fields, vegetable or fruit crops and without vineyards. It then travels through the rock for around twelve years. According to Mineralquellen Mels AG, no pesticides are detectable in it, as the original purity of any natural mineral water requires.

More on this in the Piz Sardona Academy.