Frequently Asked Questions - Recommended arsenic treatment methods

  • Surveyed treatment providers in New Jersey and the New Jersey Department of Environmental Protection recommend adsorption systems to treat arsenic in private wells.  The biggest decision buyers are faced with is whether to treat all the water in the house or a single tap in the kitchen.
  • The preferred system is a Whole-House treatment system with two tanks in series, which is often called "Point-of-Entry" (POE) because it treats all water in the home near the point where the water enters the home.
  • The other type of treatment is single tap treatment, which is often called "Point-of-Use" (POU) because the treatment unit is usually near the single tap used for drinking and cooking water.
  • The recommended arsenic treatment system is a Whole House two-tank adsorption system with the following components:
  1. Two Whole-House arsenic treatment tanks in series with a high capacity arsenic treatment media
  2. A sampling port between the two arsenic tanks
  3. A 5 micron sediment pre-filter before the arsenic tanks (depending on whether other water treatment elements are in place before the arsenic tanks)
  4. A 5 micron sediment post-filter after the arsenic tanks
  5. A water meter
 
An effective system also needs to be maintained. To qualify as a well maintained system, a water test must be conducted yearly from the kitchen sink and the sampling port between the two arsenic tanks.  If the arsenic between the tanks is greater than 5 mcg/l, your water treatment professional should remove the worker tank, replace it with the safety tank and install  a new safety tank.  

One-tank POE system disadvantages:

    • With no back-up/safety tank homeowners are at risk of drinking water with unhealthy levels of arsenic during the period after the arsenic begins to break through the treatment media and before the next testing.

One-tank POE system advantages:

    • Cheaper in the short term
  • A one-tank POE system is cheaper in the short term, but with no back-up/safety tank homeowners are at risk of drinking water with unhealthy levels of arsenic during the period after the arsenic begins to break through and before the next testing.
  • The water goes through the first tank and then through the second tank.  We call the first tank the "worker tank" because it does the most work removing arsenic. When the worker tank is new it will remove all the arsenic, but after about one year (depending on the arsenic level and how much water is used), the worker tank's arsenic removal efficiency will start to decline and some arsenic will start to break through the worker tank. When this occurs, the second tank will remove the arsenic, and this is why we call the second tank the "safety tank".
  • Without the safety tank you would be exposed to the arsenic getting through the worker tank.  With only a one-tank system you won't know you're being exposed to arsenic until the next water test is obtained.
  • A properly installed and maintained two-tank POE system will reduce your arsenic exposure to zero, which is the EPA maximum contaminant level goal for arsenic. A one-tank POE system can't meet this goal.
  • A two-tank POE system is also more economical over the life of the system. With one tank you'll need to change the tank as soon as the concentration gets near 5 mcg/l. Otherwise you will be exposed to arsenic levels above the state standard. However, with a two-tank POE system, you can safely conduct once per year sampling and not need to replace the worker tank until the concentration after the worker tank exceeds 5 mcg/l.  Even if the concentration after the worker tank goes up to 10 or 20 mcg/l, the safety tank will remove all of the arsenic before it reaches the taps in your home.
  • The typical two-tank POE arsenic water treatment system is 4-5 feet tall and requires a floor area of about 2 feet by 3 feet.
  • Most homeowners find space for these systems in their basement near the well water pressure tank.
  • It's important to realize that if you choose a less expensive arsenic treatment media it may have a lower capacity to absorb arsenic. This means you may need to replace the tanks more often and the system will likely cost you more over the long term.
  • DEP strongly recommends a 5-micron pre-treatment sediment filter to prevent any dirt or geologic materials coming up from the well from clogging or fouling the arsenic water treatment equipment. 
  • If a water softener or other treatment unit capable of removing dirt or other particles will be located before the arsenic water treatment unit, and the well water is not especially dirty, then the pre-treatment sediment filter can be considered optional.
  • A 5-micron size post-treatment sediment filter is essential to prevent any particles of treatment media, which may be highly enriched in arsenic, from getting into your drinking water supply. DEP staff have observed many cases of arsenic treatment media breakthrough.
  • 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).