Arsenic in Well Water
As in groundwater can occur in two different forms, Trivalent (Arsenic III or Arsenite) and Pentavalent (V or Arsenate). It is important to understand which form exists before choosing a water treatment device. Thus I am unable to answer this questions without that information.
Those individuals with pentavalent arsenic can select either reverse osmosis or distillation. Individuals with trivalent arsenic can select distillation, or consider adding chlorine to their water to convert the trivalent arsenic to pentavalent arsenic.
Whole house treatment is costly and may produce a significant quantity of brine (if using RO) that will need to be disposed of. So, make sure you need to treat the entire house before investing in the treatment device.