16. What water treatment options are only effective at removing Arsenic 5?

  • Reverse Osmosis 
    • Reverse osmosis is not effective at removing Arsenic 3.  There is no simple and affordable test commercially available to determine which arsenic species is present so the species of arsenic present is usually unknown, though there is a rule of thumb which can help (see FAQ#15).
    • Reverse osmosis can be an effective Point-of-Use (POU) treatment system for drinking and cooking water when Arsenic 3 is not present
    • POU reverse osmosis has been found to be a good backup in combination with a Whole-House POE arsenic removal system when only Arsenic 5 is present.
    • Whole-House reverse osmosis is not recommended due to cost, size of system, and the fact that reverse osmosis treated water should not be run through copper plumbing.
  •  Anion Exchange Systems
    • Anion exchange systems are not effective at removing Arsenic 3. There is no simple and affordable test commercially available to determine which arsenic species is present so the species of arsenic present us usually unknown, though there is a rule of thumb which can help (see FAQ#15).
    • The anion exchange system requires regular maintenance that involves purchasing water softener salt to keep the brine tank filled. If the salt level is not maintained, the system will stop removing arsenic and will dump the previously removed arsenic into the home's water at a very elevated concentration.
    • When an anion exchange system runs through a regeneration cycle all of the arsenic captured by the system will be flushed out of the tank and discharged somewhere near the home, usually to the home's septic system.
    • For the above reasons, we strongly recommend against using anion exchange for arsenic removal even if only Arsenic 5 is present.
    • However, for well water with a high pH (pH>8.5), anion exchange can be an effective tool for lowering pH and can be used as pre-treatment in combination with a Whole-House Point-of-Entry (POE) arsenic removal system (see FAQ# 27).