Chlorothalonil in water: why the canton of Vaud is affected

Chlorothalonil is an agricultural fungicide that was used for decades in Switzerland, particularly in the arable farmland of the Plateau. In 2019, the federal authorities reassessed the substance and classified several of its metabolites as “relevant” for drinking water; its use has been banned since 1 January 2020. The story could have ended there. But chlorothalonil’s metabolites, the molecules produced as it degrades in the soil, have one peculiarity: they are highly persistent and highly mobile. Years after the ban, they are still found in the groundwater that supplies part of French-speaking Switzerland.

Why the canton of Vaud is on the front line

Geography explains it: the arable regions sit above the Plateau’s aquifers, precisely where chlorothalonil was used most. Several communes, notably in northern Vaud and the Broye, have recorded exceedances of the 0.1 µg/L maximum value set for relevant metabolites in drinking water. The distributors concerned have responded: dilution with less affected resources, interconnections between networks, new catchments and, in some cases, activated-carbon treatment. The situation therefore evolves commune by commune; for the current state of your network, refer to the communications of your distributor and the canton, which publish the results of sampling campaigns.

What this means for your glass

Let’s stay factual: exceeding the threshold does not make water immediately dangerous, the 0.1 µg/L value is a deliberately low precautionary value applied to pesticides and their metabolites in drinking water. But it expresses a simple principle: these substances have no place in the water we drink, and their prolonged presence in groundwater is a reminder that water quality plays out over decades.

What a household can do

At the scale of a home, two approaches exist:

• Activated carbon partially retains certain chlorothalonil metabolites, with effectiveness varying by molecule, a useful first step, especially combined with the retention of chlorine and classic pesticides offered by an EMMO filter.
• Reverse osmosis remains the most complete answer: the membrane of the E400 reverse osmosis unit rejects 96% of dissolved salts and substances, metabolites included. Direct-flow and tankless, it treats water at the moment you draw it.

In practice

If you live in an affected commune of the canton of Vaud, the sensible approach has three steps: consult the analyses published by your distributor, assess your usage (drinking, cooking, baby bottles), and choose the right equipment. EGBT SA installs either solution in a single visit of about two hours, without building work, and handles annual maintenance, in Geneva and across the canton of Vaud, from Yverdon-les-Bains to Nyon.

Discover the E400 reverse osmosis unit →