Contaminants in drinking water can enter a person’s body by:
- Drinking the water,
- Eating food prepared with the water (such as boiling pasta or making infant formula),
- Breathing in chemicals released into the air while showering, and
- Absorbing chemicals through the skin while bathing.
Different contaminants can cause different health effects. The level at which a contaminant becomes harmful is different for every contaminant.
If a person is exposed to a contaminant, it does not necessarily mean that their health will be impacted. The risk from exposure depends on the specific contaminant, the level of contaminant, how it entered your body (by drinking, breathing, and/or touching), how often exposure occurred, how long exposure lasted, and your health. Drinking water contaminants are more likely to cause harm during childhood and pregnancy as well as among adults over 65 and individuals with weakened immune systems.
Where does my drinking water come from?
In the United States, people receive their drinking water from either a public water system or a private well.
Public water systems
Public water systems are defined by having at least 15 service connections or serving at least 25 people per day for at least 60 days of the year. Public water systems get their water from two main sources: surface water (such as streams, rivers, and lakes) or groundwater (aquifers).
There are two types of public water systems:
- Community Water Systems provide water to people year-round. Most people in the United States receive their water from a Community Water System.
- Non-community water systems do not serve the same people year-round. These include campgrounds and schools with their own systems.
A list of all community water systems in Massachusetts and the cities and towns they serve is provided here.
Private wells
A private well provides water for fewer people than a public water system, usually a single home. Nearly all private wells use groundwater. In Massachusetts, over 500,000 people rely on private wells for their drinking water.
How is drinking water regulated?
By law, public water systems must test the water for bacteria and contaminants on a regular basis. The U.S. Environmental Protection Agency (EPA) regulates public water systems by setting a limit on the highest level of a contaminant that is allowed, called the Maximum Contaminant Level (MCL). Regulated contaminants include chemicals, bacteria, and radioactive compounds.
In Massachusetts, the Department of Environmental Protection (MassDEP) oversees public water systems using a combination of EPA and state-specific MCLs. Private wells, however, are regulated at the community level by local health officials and testing is the responsibility of the homeowner. MassDEP recommends that all homeowners use a state-certified laboratory to test water from their private well.
What is a maximum contaminant level (MCL)?
An MCL is the highest level of a contaminant that is allowed in drinking water. It is an enforceable standard, set at a level that is safe to drink for an entire lifetime. To set an MCL, EPA evaluates studies on health effects, the occurrence of a contaminant (where it is found and at what levels), and the effectiveness and cost of available treatments to remove the contaminant.
MCLs apply to all community water systems. However, testing requirements may vary for a contaminant (or contaminant group) based on the type of source water and on previous testing results. Surface water systems typically test more frequently than groundwater systems because the occurrence of contaminants changes more often. Systems that do not detect contaminants or detect them at levels much lower than the MCL may be approved by MassDEP to test less often. Testing frequency may also vary depending on the size of the population served and type of water treatment.
Drinking water standards and testing requirements can change over time. EPA periodically reviews existing regulations to consider new information on health effects, treatment technologies, testing methods, and contaminant occurrence. Based on this information, EPA may revise existing regulations or develop new ones for unregulated contaminants. When a new MCL is established or an existing MCL is revised, EPA publishes a draft MCL in the Federal Register and provides opportunity for public comment.
How are private wells tested?
There are no federal or state requirements to test private well water (although a mortgage lender may ask for it). In Massachusetts, local Boards of Health and local Health Departments have the authority to regulate private wells. They can set rules for their location, construction, water quality, and quantity.
MassDEP recommends that all homeowners with private wells test their wells using a state-certified laboratory. Tests should check for common natural and man-made contaminants found in Massachusetts private well water with additional tests considered depending on nearby land uses. It is not necessary to do all the tests at once. For more information, visit MassDEP’s Private Well Testing Guide.
How does MA EPHT track drinking water quality in public water systems?
MA EPHT provides information on community water systems, including the number of people served, and tracks the following ten drinking water contaminants using data provided by MassDEP’s Drinking Water Program:
Linking data on contaminant concentrations in drinking water with health data allows public health professionals and researchers to study potential relationships between exposure to specific contaminants and health effects. It can also inform decisions by residents, local officials, and policymakers.
The Massachusetts EPHT Program does not provide data on the quality of drinking water from private wells.
Available data
Information on drinking water contaminants (Arsenic, Atrazine, DEHP, Disinfection Byproducts, Lead Nitrate, PCE, TCE, Uranium) are available on this site. Click the Explore Drinking Water Quality link on this page to access the following drinking water quality measures in your community. The most current available data will be shown. Be sure to check the site periodically as new data are added each year:
- Annual maximum concentration by number of Community Water Systems and year of testing
- Annual average concentration by number of Community Water Systems and year of testing
- Annual maximum concentration by number of people served by the Community Water Systems and year of testing
- Annual average concentration by number of people served by the Community Water Systems and year of testing
- Quarterly average concentration by individual Community Water System or county and year of testing (Atrazine, Disinfection Byproducts, Nitrate only).
- Drinking water violations by Community Water System or community and year of violation
To protect privacy, no information is shown that could identify an individual home or family.
Additional resources
- Private wells: Information and resources help well owners learn about proper practices for safe water.
- Protect your family: A guide to water quality testing for private wells
- Find a certified laboratory for water testing