Fluoride is a widely distributed ion in the environment and, consequently, in water as well. High levels of fluoride in waters can be found in the Canary Islands because of their volcanic origin. Due to the risk and detrimental effects associated with a high fluoride intake, the content of this ion has been potentiometrically determined in 256 supply water samples from the islands of Tenerife, El Hierro, and La Palma, using a fluoride selective ion electrode. Fluoride mean concentration found on Tenerife is 4.22 mg/L, exceeding the parametric value of 1.5 mg/L set out in Spanish legislation. The consumption of 2 L of water from the studied municipalities of Tenerife would mean there is an excessive fluoride intake. The consumption of this water poses a serious risk to health. It is necessary to take action aimed at reducing the level of fluoride in the north of the island of Tenerife.
Keywords: Acceptable daily intake; Endemic fluorosis; Fluoride; Recommended daily intake; Risk assessment; Selective ion electrode; Supply water.