The facts behind a better well-water conversation.
Private wells are different from public water systems. The homeowner is responsible for understanding the water, arranging testing, and deciding what to do with the results. The statistics below bring together current Massachusetts guidance and national public-health data, with every figure linked to its original source.
This page is for reference, not a diagnosis. A changing taste, odor, color, or test result deserves a closer look at the specific home and water source.
Private well water at a glance
Massachusetts residents rely on private wells.
MassDEP says more than 500,000 people in the Commonwealth use private wells because public water is not available to them.
MassDEP Private Well Guidelines ↗Source date: Accessed October 27, 2026Bacteria and nitrate/nitrite need regular testing.
MassDEP says private-well owners should test at least yearly for bacteria and nitrate/nitrite, with additional testing guided by the home, the well, and local conditions.
MassDEP Private Well FAQs ↗Source date: Accessed October 27, 2026Other core tests are not one-and-done.
For many other contaminants, MassDEP recommends an initial test and then at least once every ten years, unless a local board of health or changing conditions call for more frequent testing.
MassDEP Private Well FAQs ↗Source date: Accessed October 27, 2026Americans get drinking water from a private well.
CDC estimates that about one in eight U.S. residents gets drinking water from a private well, a reminder that private water is a major household concern, not a fringe one.
CDC, Private Drinking Water and Public Health ↗Source date: June 2024Sampled private wells had a chemical concern.
CDC reports that about one in five sampled private wells had at least one chemical at a level that could affect health. This is a national sample, not a prediction for any individual well.
CDC, Private Drinking Water and Public Health ↗Source date: June 2024, reporting historic U.S. well samplesPeople rely on groundwater for drinking water nationwide.
USGS reports that groundwater serves as a drinking-water source for about 140 million people in the United States, including both domestic-well and public-supply users.
USGS, Status of Water-Quality Conditions in the United States, 2010–20 ↗Source date: 2023 reportTesting is how you turn a water concern into useful information.
MassDEP recommends using a state-certified laboratory for private-well testing. Before ordering tests, homeowners should also check with their local board of health because local rules can add requirements.
If a change shows up after heavy rain, a drought, a repair, or a plumbing modification, MassDEP lists those as reasons to consider more frequent testing. A result can guide the next step, whether that means a plumbing check, a well professional, or water treatment matched to the concern.
Explore MassDEP private-well resources ↗How to use this reference.
Each fact above comes from a named public source and is linked directly to that source. Massachusetts-specific figures and testing guidance come from the Massachusetts Department of Environmental Protection. National figures come from the Centers for Disease Control and Prevention and the U.S. Geological Survey. The page is reviewed regularly, with the source date displayed beside each statistic.
Numbers can describe a broad population or sample. They cannot determine the condition of an individual private well. For a home-specific decision, use a certified laboratory result and the guidance of the appropriate local or state resource.
JC Plumbing & Filtration. “Massachusetts Private Well Water Facts & Testing Statistics.” Updated October 27, 2026. https://jcplumbingfiltration.com/resources/private-well-water-facts
Start with what your water is telling you.
If you are noticing odor, staining, sediment, or a change in water quality, JC Plumbing & Filtration can help you talk through the practical next step for your home.