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This is a very tricky one. It is possible to remove fluoride but can only think of very expensive solutions e.g. by Reverse Osmosis or a specific ion exchange resin.
Could attempt to try and partially solve this one with dilution from other sources with a lower fluoride content.
As always there is a need to balance risks to health - what are considered to be 'dangerous' levels here and what are the other risks to health. I mention this as quite often safety standards for chemicals have a lot of 'safety factor' built in. If the risk from microbial disease is great then the risk from fluoride may be relatively small. Without results I cannot comment further.
I would expect really high fluoride levels to be localised - whatever the source of the fluoride. So moving location may solve the problem or at least reduce concentrations. The other thing that may help is to pump the borehole hard for, say, several weeks? i.e. is the fluoride really in the groundwater or just localised to borehole area (contamination - e.g. by drilling muds etc.).
High levels of fluoride are fairly uncommon but expected in areas of volcanic activity (hydrothermal), mining operations for metal ores and contamination from industry (e.g. aluminium smelters particularly bad). If entirely natural then the problem is probably going to be difficult or impossible to solve - if man made then there is potential for remedies by reducing contamination.