​The main sources of fluoride in groundwater are sedimentary rocks ( for example, fluoroapatite from phosphate basins ), but also igneous rocks ( granites ) and veins.

​

Thermal areas are also frequently involved.

 

Rock-groundwater contact time and chemical interactions determine the concentration of free F-.

 

Even though these concentrations are extremely variable, they can reach 5 to 8 mg/l in sedimentary basins ( Senegal, Travi ).

 

Fluoride is recognised as an essential element for the prevention of tooth decay ( fluoride toothpaste ).

 

However, regular ingestion of water with a fluoride concentration greater than 1,5 mg/l can cause problems such as bone and dental fluorosis ( brown colouring of the teeth which can lead to their loss ) : children are particularly vulnerable to this problem.

​

• WHO guideline value is 1.5 mg/l maximum of fluoride ( F- )..

​