Two Connecticuts, one state.
Homes on utility water, homes on private wells. Select a region to see who tests the taps there and what the geology can add.
What this map can and cannot tell you.
The map shows how Connecticut divides between utility water and private wells, region by region, and what the bedrock underneath tends to add. Its figures are directional estimates drawn from state and federal sources, not a survey of any single street.
What no map can tell you is what is in your specific well. Two wells on the same street can draw from different bedrock fractures and test very differently, which is why every claim here points back to the same place: your own tap.
Most homes test fine. Testing is how you find out which home is yours.
Why the bedrock decides so much.
Connecticut sits on very old rock, and the rock is not the same everywhere. Much of the state, especially the hills in the west and the northeast corner, is crystalline bedrock: granite and gneiss threaded with fractures that drilled wells draw from. The central valley runs on younger sedimentary rock, and the shoreline adds coastal deposits on top.
That variation is why some regions see more arsenic and uranium in well water than others. Both occur naturally in crystalline rock, and groundwater sitting in its fractures dissolves trace amounts. A USGS study of more than 2,000 private wells in Connecticut bedrock aquifers found 3.9 percent of samples above the EPA arsenic limit of 10 micrograms per liter and 4.7 percent above the uranium limit of 30 micrograms per liter.
Neither has a taste, a color, or a smell, and neighboring wells can differ because they intersect different fractures. The geology sets the odds; only a lab test reads your number.
Source: USGS Open-File Report 2020-1111Reading the map from your kitchen.
The map sets the questions. Your tap answers them.
The map tells you that your region runs on bedrock wells and which invisible parameters tend to come with that rock. It cannot tell you your numbers: arsenic, uranium, radon, bacteria, hardness, and pH are well-by-well facts, and no agency tests a private well for you.
A certified test closes the gap: the fast movers every year, the bedrock panel every few years. If treatment is ever needed, it follows the lab line that failed. A softener addresses hardness; filtration addresses contaminants. The two are never interchangeable.
The utility tests its system. The last stretch is yours.
The map shows your water arriving tested and regulated from a public system. What it cannot see is the stretch the utility cannot see either: your service line, your solder, your fixtures. Lead usually enters there, past everything the annual report measures.
A tap test tells you what your own plumbing contributes, with first draw sampling for older homes. Taste complaints like chlorine have simple filtration answers once the number behind them is known.
The numbers behind the map.
Private wells serve Connecticut homes, about 23 percent of residents, more than 837,000 people. No utility tests them.
Source: CT DPH, 2020 census basisIn July 2026, nine Connecticut shoreline towns were placed under a mandatory boil water order after E. coli was detected in the public supply. The order was lifted the next day. Nobody knew there was a problem until a sample was tested.
Source: Connecticut Water Co. / news reports, July 2026The EPA’s enforceable limit for PFOA and PFOS, finalized in 2024. PFAS have been detected in public water supplies across Connecticut.
Source: EPA 2024 PFAS rule · EPA UCMR 5 monitoringThe full figures, sources, and the geology behind them live on Water Awareness.
Wherever you are on the map, we drive there.
Statewide Connecticut, Farmington Valley and Litchfield focus. Call, book, or write.