Knowledge Bank

Fluoride contamination of drinking water is a significant health hazard in many parts of Tanzania, and understanding fluoride distribution is vital for future groundwater development. In the Singida region, a spatial analysis of fluoride concentrations in wells showed that fluoride distribution is primarily controlled by bedrock lithology, and most boreholes with dangerous fluoride concentrations are drilled in igneous and metamorphic rocks of the Kavirondian-Nyanzian Supergroup. Borehole productivity depends on striking water-bearing fractures in the bedrock, and drilling efficiency may be improved by abandoning dry wells at depths of 50 meters, shallower than is typical for local drilling companies. Dissolution experiments performed on soil and bedrock samples from a village in the Kilimanjaro region that struggles with fluoride contamination showed that soil can be a source of fluoride to groundwater, while bedrock releases negligible fluoride. An external source like hydrothermal water is likely needed to explain observed fluoride in groundwater.