Well water problems
Arsenic in well water: you can't taste it, so test for it
The problem: invisible, and common in parts of the region
Arsenic is a natural element in certain rocks and soils. It gets into wells mostly as groundwater moves through that rock, and sometimes from past use of arsenic-based pesticides. NC DHHS states it plainly: you can't see, smell or taste arsenic.[source] A well can produce clear, good-tasting water and still be well above the standard.
The EPA set a drinking water standard of 10 parts per billion (10 µg/L) for public water systems in 2001.[source] North Carolina's environmental agency adopted the same level in 2001 and reaffirmed it in 2011.[source] Private wells aren't regulated, but 10 µg/L is the benchmark every lab report and health department uses. The standard exists because EPA has determined that inorganic arsenic is a known human carcinogen.[source]
Likely causes, and where it shows up
Most of Union County sits on the Carolina Terrane, long called the "slate belt." North Carolina's groundwater assessment found arsenic above 10 µg/L mainly in wells drilled into meta-mudstone, and lower levels in wells in meta-volcanic rock. It suggests arsenic is released from sulfide minerals in the bedrock as chemistry and pH change, and notes that shallow wells can also pick up arsenic from old pesticide use.[source] NC DHHS lists Alexander, Anson, Dare, Montgomery, Stanly and Union as counties that typically have more detectable arsenic.[source]
19.46%
of 5,154 tested Union County wells above 10 µg/L
State-lab tests, Oct 1998 to May 2019.
21.0%
of 2,993 Union County well samples above 10 µg/L
Private well samples, 2000–2011.
Source: NC Division of Water Resources, Union County Groundwater Assessment Report (2015)
18%
of 1,278 tested Stanly County wells above 10 µg/L
State-lab tests, Oct 1998 to May 2019.
2.26%
of NC wells sampled for arsenic in 2018–2019 above the standard
Statewide, for comparison.
Arsenic is much rarer in some nearby counties. It was found above the standard in 0.12% of 2,600 tested Mecklenburg wells[source] and 0.06% of 1,817 tested Iredell wells.[source] Montgomery (7.81% of 576)[source] and Anson (18.94% of 132)[source] sit in between or higher. These rates come from wells whose owners chose to test, not a random sample, and arsenic can vary between neighboring wells. Your result is the only one that counts. See the Union County and Stanly County pages for local detail.
How testing works
Arsenic is on North Carolina's required panel for new wells, so a well built since the rule took effect on July 1, 2008 should have a first result on file.[source][source] Our new-well test results guide shows how to find it. One test isn't the end, though. NC DHHS recommends testing for metals, including arsenic, every two years.[source]
- Use a certified lab. Arsenic needs a laboratory method. Home strips and in-home demos aren't a basis for treatment decisions. Our well water testing uses state-certified labs.
- Know which form you have, or plan for both. Groundwater can hold two forms, arsenic III and arsenic V. Arsenic III is harder to remove, and a routine panel usually doesn't tell you which form is present. NC DHHS advises a pretreatment step that converts arsenic to the V form before treatment.[source]
- Test the other things that affect treatment. Iron, manganese and pH can change how arsenic treatment performs. NC DHHS notes removal depends on what else is in your water.[source]
Treatment categories
NC DHHS lists four treatment types that reduce arsenic: adsorptive media, ion exchange, distillation and reverse osmosis. Pretreatment such as an iron-oxidation or manganese-dioxide filter converts arsenic to a form those systems can handle.[source] In practice, homes use one of two approaches:
- Point-of-use at the kitchen tap. Since the main concern with arsenic is water you drink and cook with, a single-tap system is often enough. Look for reverse osmosis certified to NSF/ANSI 58, or a filter certified to NSF/ANSI 53, for arsenic reduction. Check the exact model in NSF's listings.[source][source]
- Whole-house adsorptive media. For high levels, or if you'd rather treat every tap, a large tank of arsenic-adsorbing media treats all incoming water. NC DHHS notes adsorptive media produces little wastewater.[source] The media has to be replaced when it's used up.
Retesting and when to get a pro involved
Arsenic treatment fails without warning. Media gets used up and membranes wear out, with no change in taste. Retest the treated water after the system starts up, then on a regular schedule. A Care Plan includes annual retesting and filter or media changes. If your result is above 10 µg/L, your county health department and NC DHHS can also help you understand it. Talk to your doctor if you have health concerns.
Under-sink systems and whole-house media tanks both connect to your plumbing. Here's how installation works.
Questions we hear
Can I tell if my well has arsenic without a test?
No. Arsenic has no color, taste or smell. Only a certified-lab test tells you, and NC DHHS recommends retesting metals every two years.
My neighbor's well is fine. Does that mean mine is too?
Not necessarily. Arsenic depends on the rock your well draws from and how deep it's cased, and it can vary from one well to the next. Test your own well.
Do I need whole-house treatment for arsenic?
Often not. Most people treat drinking and cooking water with a certified point-of-use system at the kitchen tap. Whole-house media is an option for high levels or for anyone who wants every tap treated. We'll walk through both with your numbers.
Will any water filter remove arsenic?
No. Many common filters aren't designed for arsenic. Only use a product whose exact model is certified for arsenic reduction in NSF's listings, and confirm with a retest of the treated water.
Where we serve
Start with an honest answer about your water.
Tell us about your home and water source. We'll recommend testing first, and only the equipment your results support.