In parts of Northern Ghana fluoride concentration in groundwater for drinking is high. How can it be removed ?

The consumers of the water with high levels of groundewater fluoride (between 1.5 and 4 mg/l) live in dispersed settlements and are provided with boreholes fitted with handpumps. The average depth of the borehles is about 30m, with average yields of 50l/min. The geology ranges betwenn moderately weathered to fresh granite. Normally about 300 people depend on one borehole. People living in these communities are mostly illiterate low income farmers who engage in subsistence farming around their houses. Currently most children in the area have been affected by the fluoride. The children have brownish teeth as a result of the fluoride.