Notions of biological and chemical risks

We need to distinguish five types of circumstances that can lead to disease.

• Direct contact with water and aquatic pollutants during bathing, hygiene treatments, etc., as in the case of swimming. 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, with a few exceptions (dissolution of compounds present in the geological environment, such as fluorine and heavy metals, and various agricultural, urban and industrial pollutant discharges), generally lower than the microbiological risk, the level of which depends on a country's level of development.

• ...