Arsenic in Well Water: How to Test a Private Well and What the Results Mean
The federal arsenic limit was a compromise from the start. In 2001, EPA adopted a lower standard for arsenic in drinking water, with the new standard of 10 parts per billion (ppb) replacing the old standard of 50 ppb. If your water comes from a private well, that limit doesn’t apply to you, though it is still the best yardstick you have.
Who is responsible for your well water?
You are. More than 43 million people, about 15 percent of the U.S. population, rely on domestic (private) wells. According to USGS, the quality of that water is not regulated by the Federal Safe Drinking Water Act or, in most cases, by state laws. Instead, individual homeowners are responsible for maintaining their wells and monitoring the water.
In practice, testing is up to you unless someone else asks for it. That gap matters because arsenic gives no warning. It has no smell, taste or color when dissolved in water, even at high concentrations. EPA has classified arsenic as a human carcinogen, and long-term exposure has been linked to cancer, cardiovascular disease, immunological disorders and diabetes.
Where does the arsenic come from?
Mostly from the ground beneath you. USGS notes that metals and metalloids are trace elements that occur naturally in the Earth’s crust, and some can be toxic or cause cancer. Arsenic is one of the substances that ends up in well water this way.
Geology makes some regions much more affected than others. Arsenic occurs naturally in many parts of the United States, including New Hampshire and other areas of New England, and it was mined commercially in New Hampshire during the 1800s.
The numbers there show how uneven the risk is. Wells drilled into New Hampshire’s bedrock fractures have about a 1 in 5 probability of containing arsenic above 10 ppb. Because that bedrock is so heavily fractured, wells only about 50 feet apart can have very different water quality. Your neighbor’s clean test result tells you little about your own well.
Source: New Hampshire arsenic fact sheet, statewide distribution in bedrock wells.
How the 10 ppb number came about
The EPA standard is written for public water systems, not for private wells. On EPA’s rule history page, the standard was adopted on January 22, 2001, at 0.01 mg/L or 10 ppb, replacing the old 50 ppb standard. Water systems had to meet it by January 23, 2006.
| Date | Event | Impact |
|---|---|---|
| 1996 | SDWA amendments | Congress directs EPA to propose a new arsenic rule by January 1, 2000 |
| June 22, 2000 | EPA proposes 5 ppb | Comment requested on 3, 10 and 20 ppb |
| January 22, 2001 | 10 ppb standard adopted | Replaces the 50 ppb standard |
| March 20, 2001 | EPA announces reassessment | Effective date postponed to February 22, 2002 |
| October 31, 2001 | EPA keeps 10 ppb | Standard stands |
| January 23, 2006 | Compliance deadline | Water systems must meet 10 ppb |
When EPA confirmed the standard, Administrator Christine Todd Whitman said that “the 10 ppb protects public health based on the best available science and ensures that the cost of the standard is achievable.” Just keep in mind that it is a threshold for taking action. It doesn’t mean levels below it carry no risk.
Testing your well and reading the result
EPA advises testing annually for total coliform bacteria, nitrates, total dissolved solids and pH, and testing for other contaminants if you suspect them. Arsenic is usually not part of that basic panel, so you need to ask for it. EPA says to use only laboratories certified for drinking water testing; your local health department may provide testing for free. Test again after a flood, earthquake or landslide, since these can let contaminants enter your well.
Your report should include the concentration of each substance and may show whether it exceeds a national drinking water standard. Check the units: 0.01 mg/L is the same as 10 ppb. If a result is over the standard, contact your health department and have the well re-tested to confirm before you buy any equipment.
What treatment options exist?
EPA notes that distillation and filtration may remove contaminants, but depending on the situation you may need a new water source.
Boiling is not one of them. NIEHS is blunt: you cannot remove arsenic by boiling water, and chlorine bleach disinfection will not remove arsenic either. Neither will a water softener.
New Hampshire’s environmental agency, in a fact sheet for well owners, describes the main options:
| Option | How it works | Trade-offs |
|---|---|---|
| Point-of-use adsorption cartridge | A filter at the kitchen sink or another dedicated faucet | If arsenic III is present, a pre-oxidation cartridge should be added, which makes the cartridge last three to five times longer; equipment from about $150 |
| Point-of-use reverse osmosis | Pressure pushes water through a membrane that holds back dissolved arsenic | Removes 60 to 65 percent of arsenic III, against more than 98 percent of arsenic V, unless a pre-oxidation cartridge is added; from about $150 plus installation |
| Whole-house (point-of-entry) treatment | Treats all water entering the home | Mainly needed for iron, manganese, hardness or sulfide; for arsenic, the agency calls point-of-use devices the most cost effective and simplest solution |
Getting your well tested, confirming any high result and checking that treatment is actually working are all up to you.
Sources
- semspub.epa.gov – “FACT SHEET: ARSENIC IN DRINKING WATER - epa.gov”
- epa.gov – “Protect Your Home’s Water” (2015)
- usgs.gov – “Arsenic and Drinking Water” (2019)
- epa.gov – “Drinking Water Arsenic Rule History | US EPA” (2015)
- semspub.epa.gov – “ARSENIC IN NEW HAMPSHIRE (NH) WELL WATER”
- 19january2017snapshot.epa.gov – “Chemical Contaminant Rules | Drinking Water Requirements for States and Water Systems | US EPA”
- niehs.nih.gov – “Arsenic”