1. Notions of biological and chemical risks

We must distinguish five types of circumstances that can lead to illness or discomfort:

• direct contact with water and aquatic pollutants during bathing, hygiene treatments, etc. This is the case with bathing. There may be a chemical risk, but it is much lower than the biological risk (bacteria, viruses, amoebae, etc.);

• ingestion of drinking water: water for drinking or food preparation (tea, coffee, soups, etc.). Here too, the chemical risk is generally lower than the microbiological risk, the level of which depends on a country's level of development;

• ingestion of food contaminated by water in the receiving environment, with simple contamination or transformation and concentration of pollutants (or their metabolites) by ecosystems and contamination of the food chain (mercury,...