Reverse osmosis water filter or distiller.
Water distiller will be cheaper to buy and operate in the long run. Distill water than take the distilled water and put it though a carbon filter to take out any VOCs (volatile organic compounds) and youll have some very pure water ready to drink.
The reason you gotta put your distilled water through a carbon filter is because the VOC's have an evaporation temperature that is lower than water so it evaporates with the water. You can either throw out the first bit of distilled water that comes out or put it thorugh a carbon filter that should filter most of the voc's