Basic Information about the Arsenic Rule
Arsenic in Drinking Water
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Arsenic occurs naturally in rocks and soil, water, air, and plants and animals. It can be further released into the environment through natural activities such as volcanic action, erosion of rocks and forest fires, or through human actions. Approximately 90 percent of industrial arsenic in the U.S. is currently used as a wood preservative, but arsenic is also used in paints, dyes, metals, drugs, soaps and semi-conductors. High arsenic levels can also come from certain fertilizers and animal feeding operations. Industry practices such as copper smelting, mining and coal burning also contribute to arsenic in our environment.
Higher levels of arsenic tend to be found more in ground water sources than in surface water sources (i.e., lakes and rivers) of drinking water. The demand on ground water from municipal systems and private drinking water wells may cause water levels to drop and release arsenic from rock formations. Compared to the rest of the United States, western states have more systems with arsenic levels greater than EPA’s standard of 10 parts per billion (ppb). Parts of the Midwest and New England have some systems whose current arsenic levels are greater than 10 ppb, but more systems with arsenic levels that range from 2-10 ppb. While many systems may not have detected arsenic in their drinking water above 10 ppb, there may be geographic "hot spots" with systems that may have higher levels of arsenic than the predicted occurrence for that area.
If you are concerned about arsenic in a private well, please visit:
If you are looking for information on arsenic in treated wood, please visit EPA's Pesticides Pre-registration web site for Chromated copper arsenate.
- When does my public water system have to comply with EPA’s revised maximum contaminant level of 10 parts per billion for arsenic?
- Can my small public water system (PWS) receive an extension of the compliance date to complete needed capital improvements?
- Is the maximum contaminant level of 10 parts per billion based on total arsenic or inorganic arsenic?
How does arsenic get into my drinking water?
Because it occurs naturally in the environment and as a by-product of some agricultural and industrial activities, it can enter drinking water through the ground or as runoff into surface water sources.
What are arsenic’s health effects?
Human exposure to arsenic can cause both short and long term health effects. Short or acute effects can occur within hours or days of exposure. Long or chronic effects occur over many years. Long term exposure to arsenic has been linked to cancer of the bladder, lungs, skin, kidneys, nasal passages, liver and prostate. Short term exposure to high doses of arsenic can cause other adverse health effects, but such effects are unlikely to occur from U.S. public water supplies that are in compliance with the arsenic standard.
If you are looking for more information about health effects, please visit the Center for Disease Control's arsenic web site.
Is my private well at risk from arsenic?
Like many contaminants that enter drinking water supplies, arsenic is potentially hazardous at high levels. Because you cannot see or taste arsenic in water, it is up to the well owner to test for arsenic. Arsenic tends to occur more frequently in ground water supplies, especially when demand causes significant drops in water levels in certain areas. It is best to consult your local health department about this situation and ask about your area. You may also wish to talk with your state geological survey office or USDA agent.
Should I have my water tested for arsenic?
If your water comes from a municipal or privately-owned water company that has more than 15 service connections or serves 25 people more than 6 months of a year, they are already testing for arsenic in your water. If you own your own, individual well, you are responsible for testing it. Contact your local health department or look in the yellow pages in your area for a testing laboratory. Be sure they are certified to do drinking water testing. Your can also call the Safe Drinking Water Hotline at 800-426-4791 and ask for the state certification officer who can give you the names of labs in your area that can do the testing.
What types of water systems must comply with the standard?
The new standard will apply to all 54,000 community water systems. A community water system is a system that serves 15 locations or 25 residents year-round, including most cities and towns, apartment buildings, and mobile home parks with their own water supplies. EPA estimates that roughly five percent, or 3,000 community water systems serving 11 million people, will have to take corrective action to lower the current levels of arsenic in their drinking water.
The revised standard will also apply to the 20,000 non-community water systems that serve at least 25 of the same people more than six months of the year, such as schools, churches, nursing homes, and factories. EPA estimates that five percent, or 1,100 of these water systems, serving approximately 2 million people, will need to take measures to meet the revised standard.
When does my public water system have to comply with EPA’s revised maximum contaminant level of 10 parts per billion for arsenic?
January 23, 2006 is the compliance deadline for the revised arsenic standard of 10 ppb MCL.
Can my small public water system (PWS) receive an extension of the compliance date to complete needed capital improvements?
All systems were given five years from the date the rule was published (January 22, 2001) to achieve compliance. Exemptions for an additional three years can be made available to qualified systems by their state. For those qualified systems serving 3,300 persons or less, up to three additional two-year extensions to the exemption are possible, for a total exemption duration of nine years. When added to the five years provided for compliance by the rule, this allows up to 14 years for small systems serving up to 3,300 people to achieve compliance. Contact your state's drinking water agency to find out if the system can obtain an exemption to complete needed capital improvement projects.
Is the maximum contaminant level of 10 parts per billion based on total arsenic or inorganic arsenic?
The MCL for arsenic in drinking water is based on total arsenic including both organic and inorganic forms.
If you have more questions about arsenic, you may find your answer on our question and answer database.