Arsenic at the Tap–A Quick Guide

Tasteless, Odorless, Colorless–and Very Dangerous


What is Arsenic and How Does it Get into Your Water?

Element 33, the toxic metalloid better known as arsenic, has had a long and nefarious history. It occurs naturally in rocks, soil, air, and groundwater, as well as from contamination via human activity. The Environmental Protection Agency (EPA) recommends an MCL (Maximum Contaminant Level) for arsenic of no more than 10 µg/L. However, the MCL recommendation remains arguably insufficient, as studies demonstrate that levels well below the MCL have adverse health impacts. For example, a 2014 study found that children drinking well water with arsenic levels as low as 5 µg/L had significant reductions in IQ and perceptual reasoning relative to children exposed to fewer than 5 µg/L.

How Many People are Affected by Arsenic?

A Natural Resources Defense Council study reports that nearly 77 million Americans receive drinking water from systems that violate federal regulations for arsenic (> 10 µg/L MCL). Contaminant levels are of particular concern in western states, as they tend to have a higher incidence and elevated average levels of arsenic in their water systems. Additionally, it is estimated that 43 million Americans use private wells as their drinking water source. While community water systems are mandated to test for the toxic metalloid, routine testing for private wells does not usually include assessing arsenic levels.

Source: USGS

Source: USGS

If you are concerned about arsenic in your drinking water, our Tap Score home water test can help. Tap Score tests for arsenic, along with more than 100 other contaminants and returns clear, comprehensive analysis. While we’re mainly focused on water at Tap Score, it’s important to note the multiple pathways of arsenic exposure–such as foods like riceapple juice, and wine.

What are the Health Impacts of Arsenic Exposure?

Arsenic has toxic effects after acute or chronic exposure and toxicity can occur via ingestion, inhalation, and dermal absorption–that affect metabolism and DNA repair.

Acute Arsenic Exposure Symptoms:

  • Abdominal pain, vomiting, muscle pain, flushing of the skin, numbness and tingling of the extremities, progressive deterioration in motor and sensory responses, or death.

Chronic Arsenic Exposure Symptoms:

  • Dermal lesions, including changes in pigment, peripheral neuropathy, and skin, bladder, and lung cancer.

What Can I Do About Arsenic in My Drinking Water?

Because arsenic contamination does not taste or smell, it is challenging for homeowners to know if their water contains unsafe levels of arsenic. Therefore, if you have arsenic in your groundwater it is strongly recommended that you retest your well for arsenic annually and then retest if ever you notice that iron concentrations in your water are changing.       

If your water has arsenic levels above 10 µg/L, we recommend that you obtain drinking water from another source or install a home treatment device. The most common treatment methods include reverse osmosis, ultrafiltration, or distillation:

Reverse Osmosis:

Up to 95% effective at removing arsenic, reverse osmosis works by forcing water through a selective membrane, which has microscopic pores that allow water molecules through, while trapping larger inorganic molecules like arsenic.


Ultrafiltration is a type of high pressure filtration through a semipermeable membrane. Water passes through the membrane, while suspended solids of high molecular weight (such as arsenic and other heavy metals) are retained.


Distillation units boil water, gather the steam, cool it, and turn it back into water. The metals and contaminants, including arsenic, stay in the boiler and the resulting water is nearly pure. Note - simply boiling your water on the stove is NOT the same as a distillation unit; in fact, boiling your water will increase the concentration of metals!

The discrepancies between research on arsenic exposure and the current federal MCL serve as a reminder that the EPA standards are strong, but they are limited to what is deemed economically feasible and do not apply to private well systems. Before deciding to install a water filtration technology, it is important to check your tap water to ensure you choose an appropriate device. You can explore all of our home water testing options at or contact our help desk by emailing

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