Arsenic in Well Water in Northwest Arkansas
Arsenic occurs naturally in rock and soil, and it dissolves into groundwater in some geological settings. It is colourless, tasteless and odourless, so like bacteria and nitrate it belongs to the category of problems you can only find by looking.
Arsenic concentrations vary enormously between wells, even nearby ones, because they depend on the specific geology a well draws from. Regional generalisations are not much use; your own well is the only relevant sample.
Common symptoms
People describe this problem to us in these ways. You may recognise several, or only one.
- None. Arsenic cannot be seen, tasted or smelled in water
- No home test kit reliably measures it at the levels that matter
- The only way to know is certified laboratory analysis
Potential causes
Natural geology
Arsenic-bearing minerals in rock and sediment dissolving into groundwater. This is the dominant source in most wells that show it.
Geochemical conditions in the aquifer
Low-oxygen conditions can mobilise arsenic that would otherwise stay bound to mineral surfaces.
Historic pesticide use
Arsenic-based pesticides were used in agriculture historically, notably in orchards, and can persist in soil.
Industrial activity
Wood treatment, mining and certain manufacturing processes.
This one requires testing to confirm
Certified laboratory analysis, and there is no substitute. The EPA maximum contaminant level for arsenic in public drinking water is 10 parts per billion — a concentration far below anything detectable by any household means.
There is a technical point that has real consequences for treatment. Arsenic exists in two forms in water: arsenic III (arsenite) and arsenic V (arsenate). Most treatment technologies remove arsenic V far more effectively than arsenic III. Where arsenic III is present, an oxidation step is normally required first to convert it.
This is why arsenic treatment should never be specified from a total arsenic number alone. Speciation — determining which form is present — is what makes the difference between a system that works and a system that disappoints.
Treatment technologies commonly used
Which of these is right depends on what your water actually measures. These are the technologies genuinely used for this problem, not a list of everything we sell.
Reverse Osmosis Systems
RO certified under NSF/ANSI 58 for arsenic reduction. Note that certifications for RO generally address arsenic V; arsenic III requires oxidation first.
Water Testing
Including speciation where arsenic is detected.
Drinking-Water Filtration
Point-of-use treatment is the common approach where drinking and cooking water is the concern.
Well-Water Filtration
Where a broader treatment train is needed.
What does not work: boiling concentrates arsenic rather than removing it. Standard carbon filtration is not an arsenic technology. Water softeners do not remove arsenic. Sediment filters do not remove arsenic. If you have a confirmed arsenic result, the treatment has to be specified for arsenic specifically.
Questions we are asked about this
How often should I test my well for arsenic?
Arsenic comes from geology, which changes slowly, so it does not need the annual attention that bacteria does. A baseline test is worthwhile for any private well, with retesting if the well is deepened or reworked, if a new well is drilled, or if nearby wells are found to have it.
Is there a safe level of arsenic?
The EPA sets an enforceable limit of 10 ppb for public water systems, balancing health protection against treatment feasibility. The health-based goal is zero. Questions about what a specific result means for your household belong with your physician or the Arkansas Department of Health.
Will my whole-house filter remove arsenic?
Not unless it was specifically designed and certified for arsenic. General sediment and carbon filtration does not address it.
My neighbour's well has arsenic. Does mine?
Possibly, and it is a good reason to test — but not a certainty. Wells drawing from different depths or different formations can differ substantially over short distances, which is particularly true in the fractured geology of the Ozarks.
We work across Northwest Arkansas
City water and private wells, in Benton, Washington, Madison and Carroll counties.