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Arsenic is a natural component of the Earth’s crust and is usually bound to an iron pyrite mineral. It can be released from the minerals and become free in solution or water under certain chemical reactions, especially in reducing conditions where there is not much oxygen.
You cannot see, taste, or smell arsenic in water, so testing is the only reliable way to know how much is in your drinking water. Arsenic is listed as a primary contaminant by the USEPA because high levels of arsenic can have potential health effects. Since it can be harmful to human health, it is important to be aware of its presence and take necessary precautions.
What are the effects of arsenic in well water?
Arsenic is a concern in well water because it can pose serious health risks including:
Skin problems
Cardiovascular disease
Certain types of cancer
When should I test for arsenic in my well water?
The United States Environmental Protection Agency (USEPA) has set a maximum contaminant level (MCL) of 10 parts per billion (ppb) for arsenic in public drinking water supplies. If your well water exceeds this limit, it is considered unsafe to drink.
To ensure you are protecting your family’s health, we have developed a set of recommendations for testing that are provided in our article, "What do I need to know about sampling my well water?" , that includes arsenic. When testing your well water you will very rarely be testing for only one thing, like arsenic, and instead testing for a suite of constituents that are important to identify if in your drinking water.
What treatment should I use if there’s arsenic in my well water?
Once you test and have decided to treat your water to remove arsenic, the Minnesota Department of Health has developed a Home Water Treatment Guide that covers treatment for any common constituent in well water. The most important advice we can provide you is if you are going to add treatment to your home water system, be sure the treatment device has been certified to remove arsenic by an independent third-party certification organization.
Does reverse osmosis remove arsenic from water?
Arsenic can be challenging to remove sometimes, likely due to the nature of the arsenic species in groundwater sources. Arsenic typically occurs in water in two oxidation states:
As(III), “arsenic three,” arsenite
As(V), “arsenic five,” arsenate
Arsenic(III) tends to be present as an uncharged form H3AsO3, and is typically more difficult to remove than arsenic(V), which usually exists as H2AsO4- or HAsO42- (both charged species). Some consumers have had good luck improving arsenic removal by adding an oxidation step (like chlorine) ahead of the RO unit.
Where can I get more information about arsenic in my well water?
Contact your local health department – They can help you interpret your sample results and may have information on the best treatment options for your situation. If they personally aren’t able to answer your questions, they will know who to contact who will be able to help you, likely at your state health department.
Contact a water treatment professional - we would recommend contacting a water treatment professional who has been certified through the Water Quality Association’s Professional Certification Program.
State or Federal Geologic or Water Resource Agency – they may have completed field studies of your area or collected samples from water wells to map and understand the water quality in your state. In addition, they may house water well logs, including yours, or be able to provide additional information about the aquifer your well is getting water from.
Consult your well driller or drilling contractor – the contractor that drilled your well, and other local contractors, may be aware of the water quality issues nearby including high arsenic, and might have worked with other well owners in your area to solve this issue .
Research online – you should be inquisitive; it will help you significantly because there may be great information available online. Use search terms like “my state (CA, ME, IL, etc.) water well logs”, “my state groundwater quality”, or “my state well water quality”.
Contact us directly – if these other local sources don’t work out for you, we may be able to help. We may be able to provide direct assistance, and/or direct you to a technical assistance provider in your area who can help answer your questions (free service funded by USEPA).
Additional Resources
Home Water Treatment, Environmental Health Division, Minnesota Department of Health.
Farrell-Poe, K., L. Jones-McLean, and S. McLean, Well Water Testing and Understanding the Results, April 2011, Arizona Cooperative Extension.
Water Well Owners Handbook, March 2010, Oregon Water Resources Department.
Want to learn more about your private well and how to care for it?
Sign up for the free 10-week email course from PrivateWellClass.org. The class is a project of RCAP and the University of Illinois, with funding from USEPA.
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