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
- 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 depends on the contaminant, the amount of the contaminant, and how it entered the body (drinking, breathing, and/or touching). The risk also depends on how often exposure occurred and how long exposure lasted. Risk of harm also depends on a person’s health. Drinking water contaminants are more likely to cause harm during childhood and pregnancy. Harm is also more likely in adults over age 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.
MA EPHT provides a list of all community water systems in Massachusetts and the cities and towns they serve.
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 contaminants on a regular basis. This includes chemicals, bacteria, and radioactive compounds. The U.S. Environmental Protection Agency (EPA) regulates public water systems by setting a limit on the highest level of a contaminant allowed. This is called the Maximum Contaminant Level (MCL).
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. The testing of private wells is the responsibility of the homeowner. MassDEP recommends that all homeowners use a state-certified laboratory to test the water from their private well. For more information, visit MassDEP’s Private Well Testing Guide.
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 and the occurrence of a contaminant (where it is found and at what levels). They also look at 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 group of contaminants) depending on the type of source water and previous test results. Surface water systems are typically tested more frequently than groundwater systems. This is because the occurrence of contaminants changes more often. Testing frequency may also vary depending on the size of the population served and type of water treatment. 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.
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. When a new MCL is established or an existing MCL is revised, EPA publishes a draft 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. However, some mortgage lenders may ask for it. In Massachusetts, local Boards of Health and local Health Departments 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 contaminants found in Massachusetts private well water. Additional tests should be 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. This includes the number of people served and data for the following ten contaminants:
Why does MA EPHT track drinking water quality in public water systems?
Tracking levels of drinking water contaminants alongside health data allows us to better understand possible impacts of exposure on health. This can inform decisions by residents, local officials, and policymakers.
Available data
Use the Explore drinking water quality link on this page to access the following drinking water quality measures for community water systems:
- Community water systems and number of people served
- Annual maximum concentration by number of Community Water Systems and people served
- Annual average concentration by number of Community Water Systems and people served
- Quarterly average concentration by individual Community Water System or county (available for atrazine, disinfection byproducts, and nitrate only)
- Drinking water violations by Community Water System or community
The most current available data will be shown. Be sure to check the site periodically as new data are added.
Additional resources
Massachusetts
- DPH Drinking Water: Learn about safe drinking water and environmental exposure
- MassDEP What's in my drinking water?: General information on drinking water from public supplies and private wells
- MassDEP Is there lead in my tap water?: General information on lead in drinking water, how lead gets into drinking water, and ways to reduce exposure
- MassDEP Private Wells: Information and resources to help owners of private wells learn about proper practices for safe water
- MassDEP Guide to Water Quality Testing for Private Wells: Recommended water quality testing for private wells
- MassDEP Certified Laboratories for Water Testing: How to find a certified lab for private well testing
- MassDEP Drinking Water Contaminants Information for the Public: Information about contaminants in drinking water
- MassDEP Drinking Water Information for Consumers: Resources on drinking water safety for consumers
- MassDEP Public Drinking Water System Operations: Regulations and guidance for public water supply operators