Most well owners in Maine test their water in the winter, if they test at all. That timing quietly works against them. Research out of the University of New Hampshire found that bacterial contamination in private wells is at its highest during the summer, with the worst readings coming from samples taken when temperatures climb above 90°F. The lowest readings showed up in February and March — exactly when many homeowners happen to collect a sample and walk away reassured.
That gap between when people test and when bacteria actually peak is a real problem. In 2023, Maine’s Drinking Water Program recorded more than 40 instances of E. coli contamination in public water systems by mid-September — roughly four times the number logged in all of 2022. Public systems are monitored constantly; private wells, which supply more than half the households in Maine, usually are not. If bacteria are surging in the systems being watched, it is a safe bet they are surging in the wells that no one is checking.
What’s Actually Happening in the Ground
Coliform bacteria are common in soil, surface water, and vegetation. On their own they rarely make people sick, but their presence is a warning: it means surface water — and whatever it carries — is finding a path into your well. E. coli is the more serious finding. It lives in the intestines of humans and animals, and a positive E. coli result confirms that fecal contamination has reached your drinking water.
Summer conditions push bacteria into wells through several doors at once. Warm temperatures speed bacterial growth. Heavier household and irrigation demand draws the water table down and stresses the well. Summer thunderstorms and heavy rain wash surface runoff — including animal waste and septic overflow — toward well casings, and a cracked cap or shallow casing is all it takes for that runoff to get in. Seasonal camps and cottages add another wrinkle: a well that sat unused all winter can harbor stagnant, bacteria-friendly water the moment the pump comes back on.
What Homeowners Should Do
Every private well should be tested for total coliform bacteria at least once a year, and summer is the right window to do it. Testing in late spring or early summer catches problems before peak demand, while a mid-summer test reflects your well under its heaviest real-world load. If your household relies on a private well, do not wait for a taste, smell, or color change — bacteria are invisible, odorless, and tasteless.
A few situations call for testing right away rather than waiting for the annual check: after any flooding or heavy runoff near the wellhead, after work on the well or pump, when you open a seasonal camp or cottage, when there is a new baby or someone with a weakened immune system in the home, and any time the water suddenly changes in appearance or smell. If a sample comes back positive for coliform, the next step is a follow-up test for E. coli to determine whether fecal contamination is present and how urgent the response needs to be.
Bacteria also matter in real estate transactions. Buyers, lenders, and inspectors increasingly want a clean bacteria result before closing, and government-backed loans such as FHA and VA financing frequently require water testing on properties served by private wells. A failed or missing test can stall a closing at the worst possible moment, so ordering it early keeps a transaction on schedule.
What Chanalytical Tests For
Chanalytical Laboratories handles bacteria testing for total coliform and E. coli, along with the fuller picture that a summer test season calls for. That includes nitrates — which climb in areas with septic systems, livestock, and lawn fertilizer — as well as arsenic and uranium, both common in Maine and New Hampshire bedrock, radon in water, and PFAS panels for the “forever chemicals” that have spread across the region’s groundwater. Standard well panels bundle the core contaminants most homeowners need in one straightforward submission, and drop-off is simple for anyone in the area.
For Home Inspectors
A local lab partnership keeps transactions moving. Chanalytical offers fast turnaround and clear, readable reporting, so bacteria and full-panel results land in time for closings instead of holding them up. Working with a nearby Maine lab means fewer shipping delays and a direct line when a client has questions about a result.
For Water Treatment Companies
Independent lab verification backs up the work you install. Chanalytical supports baseline testing before a system goes in, post-installation verification that treatment is performing, and ongoing confirmation testing — giving your customers documented proof that a UV system, filter, or disinfection setup is doing its job against bacteria and other contaminants.
Test Before the Season Peaks
If your well hasn’t been tested this year, summer is the moment to do it — not the quiet months when readings look deceptively clean. Chanalytical Laboratories is Maine-based, with fast turnaround, simple sample drop-off, and support for homeowners, home inspectors, and water treatment companies across the region. Visit Chanalytical.com to get started, request a bacteria or full well panel, and find out what is actually in your water while it matters most.