Throughout the water cycle, drops of water become charged with different elements, which they may then leave behind as they pass through the subsoil.
16 September 2014

Groundwater: the transfer of pollutants to aquifers

An educational animated film produced by BRGM and the Adour-Garonne Water Agency (2014). 

© BRGM / Agence de l'eau Adour-Garonne 

A drop of water is born in the air. Liquid or frozen, it is not alone. It rubs shoulders with dust in the air, because a cloud is anything but a quiet chemical body. Gases, dioxins, pesticides, nitrates, and many more. First encounter. Some molecules are already stuck to her like glue. As soon as it's born, its composition changes. Rain takes it to the ground, with the initial baggage it is carrying. At its first destination, the ground surface, the drop of water may be tempted by several paths. In a hurry and laden with its baggage, it leaps into the arms of surface runoffs which take it her to a waterway. Being curious, it will take a short cut to the subsoil and its groundwater tables. It may come across elements already present of human or natural origin, such as iron or limestone. New chemical molecules it will transport. During its stay in the subsoil, she'll meet some nice and less nice elements. It may stay there 5-20 years, so our drop of water witnesses and records the human activities of this period. Being bold, it may take long and winding routes to reach the deep tables. It divests herself, by lack of oxygen or other chemical processes, of its molecules, the witnesses of human activity. But it has encounters of another kind that put it in contact with the molecules contained in the rock the table goes through. Once reaching these depths, it takes its time and warms up. Its stay can last thousands of years. But this long layover is beneficial. It acquires the virtues and particularities of our thermal and mineral waters. But all journeys lead to a final destination. Our drop of water will leave the table naturally via a spring, or man will take it by the hand by digging a well or boring. Sooner or later, it will join the sea whence it will start a new trip in the form of vapour.