If the fluoride is the only ...

If the fluoride is the only ion you want to remove and water has low TSS, low TOC, activated alumina and activated carbon can be used to get the fluoride lower than 1mg/l. If the fluoride in the feed water is higher than 20 mg/l, lime and alum should be used to decrease the fluoride concentration ahead of the absorption to increase the life span of the alumina filter. If other ions or TDS need to be reduced and water has low TSS , low TOC, SDI<3, maybe you want to use ion exchanger or membrane (such as RO or NF).  Electrical coagulation is an option if you have high TSS , TOC, color, smell as well as fluoride. EC can also remove some pesticides, bacteria and viruses.