I have a well with 1.9 ug/L total arsenic (As). Yes this is below the EPA action level of 10 ug/L. However, most states do have warnings indicating that longer term consumption of As below that level can still lead to health effects. So, I am looking to remove as much As as possible. RO seems to be a preferred method. I see a lot of information on its efficacy when As levels are high, but not as much info on how effective it is when As levels are low. Can anyone tell me how RO systems perform where As levels are already low?

Additional info:

  • There is some iron in the water, but there is already a water softener pre-treatment tank to take most of that out. Lack of staining in the toilet tanks would seem to confirm that it is working.

  • I don't know if it is As(III) or As(V). I am aware that will impact performance. For the sake of this question let's assume it gets converted to As(V)

  • Nitrate and chloride all test near the detection limits.

  • I am thinking along the lines of an under sink model rather than a whole house system.

  • RO systems are the best filter mediums I know of other than distilled water. RO systems take a huge amount of water to produce the extremely clean water I think 3 gallons of waste water to 1 gallon of clean. Distilled has a high energy requirement and the contaminates end up in the boiler so that or the anode have to be replaced regularly. With RO the water is forced through a membrane the contaminates are blocked by the membrane, then the system is backwashed to flush the contaminates out this is where the high usage comes from RO takes out metals and most chemicals that’s what I know.
    – Ed Beal
    Sep 17, 2020 at 1:19
  • 3 scientific panels considered 3, 5,and 10 as the limit in 2001, and they went with 10. You're well below even the most strident consideration, and filtering just to remove that is likely to strip other useful minerals from your drinking water, which likely does more harm than good. Use a brita for drinking water if you'd like, but don't worry about such low arsenic levels.
    – dandavis
    Sep 17, 2020 at 17:33


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