Private Well Water Metadata: Well Water Quality (Testing) Data


Well water quality data are from the Maine Center for Disease Control's Health and Environmental Testing Laboratory.

Dates Available:

1999 - 2019

Geographic Resolution:

County, Town


The Maine EPHT program receives well water sample data on an ad hoc basis from the Maine Center for Disease Control's Health and Environmental Testing Laboratory (HETL).


This data set supports efforts to improve public health in Maine and contributes to the U.S. CDC’s National Environmental Public Health Tracking (EPHT) Network. A key activity of participants in this network is to track and make available environmental health measures on state and national data portals. Measures derived from the data set described here can be used to compare adult and childhood cancer rates across the state, between groups of people, and over time.

The Maine Tracking Network, a member of the National EPHT Network, connects communities, public health professionals, policy makers, state agencies, and others to the data they need to monitor public health, respond to health concerns, prioritize resources for public health action, and evaluate prevention activities. Maine tracks certain health effects, exposures, and environmental hazards that have known relationships, as well as some health effects and environmental hazards that have suspected relationships. By making health and environmental data available through the Maine Tracking Network, more people have access to data they need to think critically and hypothesize about health outcomes and their relationships to conditions in the environment.

Supplemental Information:

More than half of the homes in Maine get drinking water from private, residential wells, and many Maine wells have too much arsenic or other contaminants of concern. Private well users are responsible for testing their water and treating any hazards.

The Maine Tracking Network summarizes test data for select contaminants in order to form a better understanding of what parts of the state may be at higher risk for well water contamination, and to encourage local well users to test their water.

Maine EPHT receives well water test results from the Maine HETL. These data are then reviewed manually to determine which samples were taken from the same well. The highest analyte sample result for each well is then taken to represent the raw water quality of that well.

Entity and Attribute Overview:

This dataset includes the following fields: geographic entity (county, town), analyte (arsenic, fluoride, manganese, nitrate, nitrite, or uranium), number of wells tested, percent of wells above guideline, median, 95th percentile, and maximum.

Data Limitations:

  • Sample data were obtained only from the State Health and Environmental Testing Laboratory, which may not constitute a representative collection of wells in a county or town.
  • Address information for each well was obtained from a billing database, which includes separate fields for billing address of the test requestor, and a separate field for town in which the well is located. The billing address was assumed to represent the well location, if it showed the same town as the reported town location of the well.
  • We assigned each test result to a unique well through a manual review of name and billing address information, in order to identify repeated samples taken at the same well. Due to the potential for address information to be left incomplete, as well as the potential for a well’s physical location to be different from the billing or mailing address associated with the well, this process can result in the misattribution of some sample records to the same or different wells. The extent of this misattribution is unknown.
  • The maximum concentration result among samples for each identified well was assumed to represent raw water quality from that source. Filtration status and type is often missing or not collected with sufficient detail to reliably restrict sample results to raw water samples only.

Access Constraints:


More Information:

Suggested Citation for Data Displays:

Maine Center for Disease Control and Prevention, Maine Tracking Network. Private Well Water: Water Quality. Available online: Accessed on [Date].