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Drinking Water and MTBE: A Guide for Private Well Owners

By: the United States Environmental Protection Agency

Do you have a private well?

About 42 million people in the U.S. get their drinking water from household wells, springs, cisterns, and streams (instead of getting piped water supplied by public water systems). Although the federal government does not supervise private wells, most states have requirements for home well installation. Gasoline is one of many pollution threats to the ground water that supplies your well. If you are a private well owner, the best way to make sure your drinking water is safe is to test it! More importantly, if your water supply is clean now, you can take steps to protect it from pollution in the future

What is MTBE?

MTBE (methyl tertiary-butyl ether) is a chemical added to gasoline to increase octane. Its use began in the 1970’s to replace lead in gasoline. After 1995, many metropolitan areas of the country with smog problems also added MTBE to gasoline because it helps to reduce harmful emissions from automobile exhaust. Adding MTBE to gas has been one way to meet EPA’s oxygenate mandate.

Why is MTBE a drinking water concern?

Gasoline and heating oil travel through pipelines and are also distributed by truck to above ground and underground storage tanks. Underground storage tank leaks and spills provide major sources of MTBE. In addition, people store gasoline in cars, boats, planes, lawn mowers, chain saws, generators, and off-road vehicles. Therefore, farm and residential releases, car accidents, spills, boats, and storm water runoff also release gasoline into the environment. MTBE moves quickly through soil, dissolves easily in water, and takes longer to break down than some other chemicals.

Could MTBE be in your water?

The US Geological Survey has found MTBE in ground water in 24 states, though gasoline with MTBE poses a risk wherever it is used, transported or stored. The USGS has found MTBE in water roughly five times more often and at higher concentrations in areas of the country where MTBE has been used as a fuel additive to reduce pollution. Your local health department may know if people are finding MTBE in your area. For most people, water with MTBE in very low concentrations tastes and smells “nasty,” bitter, or like turpentine. However, natural or water treatment chemicals can hide or increase taste and odors in drinking water. Typically, the levels of any contaminant increase very slowly in a well as the contaminated water moves from the source into the well. The result is that people drinking the water every day may not notice a change in the taste or odor. Over time they may become accustomed to the taste and smell. You may discover the problem only when someone who has not been drinking contaminated water (perhaps a friend from across town or an out-of-town visitor) notices that the water tastes or smells funny. If you suspect contamination, you may want to pay to get your water tested for MTBE. It costs about $150 per sample, and your state can give you a list of laboratories certified to test for MTBE. EPA recommends yearly testing of private water supplies for nitrate and coliform bacteria. Some states recommend other testing and your local health department may do these water quality tests for you.

How much MTBE is too much?

Most people can taste and smell MTBE in very small amounts. According to EPA’s Drinking Water Advisory, EPA reviewed health effects studies in 1997 and noted that drinking water with MTBE levels of 20 to 40 “parts per billion” (acceptable taste and odor) would probably not pose health risks. MTBE at 20 ppb in water is about the same as one drop in 500 gallons of water. EPA has efforts underway to fill some of the data gaps on health effects of MTBE and the extent of its occurrence in drinking water supplies. Current data on MTBE levels in ground and surface waters indicate widespread and numerous detections at low levels of MTBE. However, in studies to date, only about one percent of the ground and surface water testing positive for MTBE has levels higher than 20 ppb. Leaks and spills from storage tanks have caused a limited number of drinking water wells to have high concentrations of MTBE. Keep in mind that gasoline contains many chemicals, some of which could be in higher concentration in your water and a much more serious health concern. Immediately contact your local health officials if your water tastes or smells suspicious, and remember to test!

What can you do if you have MTBE contamination?

Make sure that you get a “certified treatment system” and consult with resources listed at the end of this brochure before you purchase a product. One not-for-profit, non-government organization, NSF International, certifies products to meet national and international standards. (

How can you protect your drinking water from pollution risks?

MTBE in gasoline is just one of many types of chemicals that can contaminate your drinking water if not properly used and stored. In addition to gasoline, pesticides, herbicides and other chemicals are used on farms and around households. Use chemicals only as directed by the manufacturer, never apply more than is recommended, and follow proper clean up procedures. Don’t build stockpiles! Stockpiling excess chemicals near your home or on your farm could be a contamination problem waiting to happen. Protect your ground water supply when you build, modify, or close a well. Inspect septic systems, maintain your well cap and surface seals, keep well maintenance records, and do not drink from flooded wells. Take preventative steps to avoid contamination from fuel stored in an underground or above-ground storage tank. Use the checklist provided in this brochure to determine if you need to take action based upon your current or past use and storage of gasoline. Use the Home *A* Syst and Farm *A* Syst Pollution Assessment Programs to assess the risk of gasoline and chemical use and storage on your farm or near your home. On the internet access (click on “search” then select “Petroleum Product Management” or “Private Drinking Water Supply” under the Household Topic Search to find worksheets developed in your state or region). To find program contacts in your state,  call 608-262-0024.

How real is the threat of MTBE contamination?

The Environmental Protection Agency and many scientific organizations continue to study the health risks and total environmental threat from gasoline containing MTBE. Fourteen states – nine of which are not required to use a fuel additive to limit air pollution in certain areas, have partially or completely banned the use of MTBE within their borders or made other regulations on its use. Even if MTBE is banned, it will be many years before it is eliminated from the environment. According to a report in the March 2001 Successful Farming magazine, even a minor spill of gasoline containing MTBE is a big threat to ground water supplies. In one instance, just ten gallons of gasoline containing MTBE was spilled as a result of an automobile accident on one person’s property. This single event led to MTBE contamination of the water supply for twelve families.


You can protect your water supply through good practices that prevent contamination and by testing your water regularly. There is a great deal of information and there are many services available on the World Wide Web if you have a computer and an internet service provider. You can get much of the same information by calling the telephone numbers listed for the resources below. The US EPA and many states have free printed materials about MTBE and other water related topics.