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Arsenic in Private Drinking Water Supplies

How to Proactively Protect Your Household from an Invisible Contaminant

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Updated:

July 17, 2023

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Arsenic is an invisible contaminant that can be found in groundwater supplies. Photo: Penn State

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Arsenic is a chemical element that occurs naturally in some rocks and sediments in Pennsylvania. When water comes in contact with these geologic materials, some arsenic may dissolve and enter groundwater that is used as a source of drinking water. Less commonly, industrial processes or certain land uses, such as mining or old orchards with pesticide residue, can be a source of arsenic in groundwater.

Arsenic in drinking water is problematic because it is toxic to humans, even at low levels. The EPA standard or maximum contaminant level (MCL) for arsenic in drinking water is 10 micrograms/liter (10 parts per billion or ppb). Public water systems are required to monitor and comply with the arsenic standard, but Pennsylvania has no statewide regulations requiring private well owners to have their wells tested.

Drinking water that contains arsenic above 10 ppb can lead to serious health effects, including cancers, especially among children and other sensitive populations. Arsenic has no detectable odor, taste, or appearance, so it is impossible to know whether it is present without testing. Many well owners optimistically assume water is safe if they do not see, taste, or smell anything unusual. Consequently, well owners may be unaware if their drinking water contains arsenic.

Location of sampling sites and associated reported arsenic concentrations in groundwater in Pennsylvania, 1969–2007. (N, number of samples. Arsenic concentrations are shown as elevated if greater than or equal to 4ppm or 4.0 micrograms per liter. Data from Low and Chichester (2006) and Low and others.

Background arsenic is variable throughout Pennsylvania. A 2012 US Geological Survey analysis of data from over 5,000 state wells from 1969 -2007, found that nearly 8% of groundwater samples contained arsenic levels at or above 10 ppb. The only way to know for sure that your water is safe is by testing using a certified lab that is qualified to test for arsenic. You can use the Penn State lab or look for other certified labs (Accurate as of July 2023. Please check for updates.)

If certified testing indicates the presence of arsenic at or above the MCL of 10 ppb, well owners may need to install an appropriate home treatment device or connect to a public water supply if nearby. It is important to check references and consult several reputable water treatment professionals for the best recommendation.

When selecting a treatment system, it may also be necessary to test for and treat additional water contaminants that would interfere with arsenic removal. You will also need to decide whether you need a point-of-use system at a particular faucet or a whole-house system. Typically, arsenic is only a health risk when ingested, but not when using water for other household uses, such as showering or laundry, so many households just install treatment devices at outlets used for drinking and cooking water. Finally, before you purchase any treatment devices, it is essential to understand the ongoing maintenance needs for the system, and the cost and schedule for replacement components.