Public water utilities in the United States are required to test for roughly 90 regulated contaminants and publish the results to every customer in an annual Consumer Confidence Report. The system is imperfect, but the floor is real — the moment a public utility's arsenic creeps over 10 ppb, somebody has to fix it, and you find out about it.
Private well owners get none of that protection. Federal regulation under the Safe Drinking Water Act stops at the property line of any system serving fewer than 25 people, and your single-family well sits well below that threshold. Testing is on you. So is interpreting the results. So is paying for treatment if anything comes back hot.
The EPA recommends private well owners test at least annually, and so does the CDC. The hard part is not the cadence — it is knowing what to test for. The list shifts with your geology, your land use upstream, the age of your home, and the season. This article is the year-by-year checklist, organized around the EPA's core panel, the regional add-ons that matter for your specific setting, and the trigger events that should pull you off the annual schedule and onto an emergency one.
For the broader picture on how testing fits with reading utility reports and choosing a filter, see How to Test Your Tap Water at Home. This guide drills into wells.
Why annual matters
A one-time test at well drilling — the test most people remember — tells you what was true on a single day, years ago, before any of the relevant year-over-year drift had a chance to occur. Well water is not a fixed input. The number on the report this year is not the number you had two years ago, and is not the number you will have two years from now.
Three reasons the cadence has to be annual rather than once-and-done:
Seasonality is real. Spring runoff after the snowmelt or the first heavy rains pushes a wave of nitrate, agricultural pesticides, and surface-source bacteria into shallow aquifers. Summer drawdown — when the water table drops because municipal demand and irrigation peak — can concentrate dissolved solids and shift mineral chemistry as the well draws from deeper, older water. Winter low-flow patterns affect iron and manganese deposition. A test in October tells you nothing about your March water.
Land use shifts upstream. A new dairy, a new septic field on a neighbor's property, a freshly tilled cornfield, a renovated road with new salt-storage runoff — anything that changes the nitrogen, microbial, or chemical load on the watershed eventually reaches your aquifer. The lag is months to years depending on your aquifer depth and permeability. Annual testing is how you catch the change before it becomes a problem you cannot reverse.
Wells age. Casings corrode. Seals fail. Surface infiltration gets easier as the well structure ages. The same well that came in clean at drilling can fail a coliform test fifteen years later because of a casing issue, not a watershed issue. Annual testing also catches those failure modes.
The CDC's private well guidance is direct on the point: test annually for the core panel, more often if you live in an area with known contamination concerns, and immediately after any event that could have changed the water.
The EPA core annual panel
The four tests the EPA recommends running every year on every private well, regardless of geography:
Total coliform and E. coli (microbiological). Total coliform bacteria are an indicator group — their presence does not necessarily mean disease-causing organisms are present, but it does mean the well has had contact with surface or shallow-source water that should not be reaching it. E. coli specifically is a marker for fecal contamination, usually from a septic system, animal waste, or sewage. The standard for both is zero detection. Any positive result is a boil-water situation until the well is shock-chlorinated or otherwise treated and re-tested.
Nitrate and nitrite. Nitrate is the agricultural runoff marker. The EPA Maximum Contaminant Level is 10 mg/L measured as nitrogen — the same threshold the federal MCL uses for public systems. Above 10 mg/L, the well is unsafe for infants under six months because of the methemoglobinemia (blue-baby syndrome) risk. The chronic adult exposure question is separate and still evolving — a growing body of peer-reviewed work is opening up effects at concentrations below the MCL. Nitrite (the more reactive form) is regulated at 1 mg/L. Both should be on the same lab report.
pH and total dissolved solids (TDS). These are the corrosion and mineral baseline. pH below roughly 6.5 means the water is acidic enough to leach copper and lead from your home plumbing — the same mechanism that drives the federal lead and copper rule for utilities applies inside your home regardless of source. TDS is a rough indicator of overall mineral content; sudden changes year-over-year can flag aquifer-chemistry shifts worth investigating.
Arsenic. The wildcard. Arsenic concentration is dictated almost entirely by geology, and concentrations vary dramatically — wells a quarter-mile apart can read very different numbers. The federal MCL is 10 ppb, and USGS modeling estimates roughly 2 million Americans drink well water above that limit, almost all in the Southwest, parts of New England, and the Upper Midwest. Annual testing is the prudent baseline; even if your zone is not a known high-arsenic area, the every-year cost is low and the cost of missing a slow rise is high.
A core annual panel through a state-certified lab runs $30 to $80. Many county health departments offer subsidized or free coliform and nitrate testing during specific months — check your state environmental or health department website before paying retail.
Region-specific add-ons
On top of the core annual panel, add the tests that match your geology and land use. These typically run on a two-to-three-year cycle once the baseline is established, but the first time through you should run all that apply.
Pesticides — particularly atrazine and its degradates. If you live in agricultural country — Iowa, Nebraska, Indiana, eastern Wisconsin, the Central Valley — pesticide contamination of shallow groundwater is documented. The USGS NAWQA program finds atrazine, metolachlor, and their breakdown products at detectable levels in shallow wells under cropland frequently enough to warrant testing. A pesticide screening panel through a state-certified lab typically runs $100 to $250.
Radon. Largely a New England, Appalachia, and mountain West concern. Radon dissolves into groundwater in regions with uranium-bearing bedrock and off-gasses into indoor air every time the water is used. The EPA does not have an enforceable MCL for radon in drinking water — proposed standards have been on the table since 1999 — but most state guidance recommends testing if you are in a known radon zone. State environmental agencies typically run radon-in-water tests for $30 to $50.
Lead. Almost always a home-plumbing issue rather than a well-source issue, since lead is rare in source groundwater. Test if your home was built before 1986 and has brass fittings, soldered copper joints, or any exposed lead solder. The federal Action Level is 15 ppb. Test first-draw water that has sat in pipes overnight — that is the worst-case sample and the one that tells you whether interior plumbing is leaching. Lab tests for lead run $20 to $40.
PFAS. Forever chemicals are a localized concern. Test if your well sits within a few miles of a current or former military base, a commercial airport with fire-training history, an industrial facility that handled PFAS-containing chemicals (chrome plating, semiconductor manufacturing, certain textile mills), or a known PFAS contamination site identified by your state environmental agency. The EPA UCMR 5 program collected PFAS occurrence data from public water systems between 2023 and 2025; many states have published the resulting maps showing where PFAS contamination clusters. PFAS testing through a certified lab using EPA Method 533 or 537.1 runs $250 to $400 and is the only way to detect the compounds at the parts-per-trillion concentrations that matter.
Iron and manganese. Aesthetic concerns rather than acute health concerns. Iron at concentrations above 0.3 mg/L causes orange staining on fixtures and laundry; manganese above 0.05 mg/L causes black staining and a metallic taste. Both shift with seasonal flow patterns in the well. Iron and manganese testing is usually bundled into the same lab order for $20 to $30.
When to test outside the annual schedule
Testing immediately, regardless of where you are in your annual cycle, is warranted when something has happened that could have changed the water. The triggers:
- A contamination event in the area. Industrial spill, agricultural runoff event after major rainfall, septic system failure on a neighbor's property, downstream news of a regional groundwater issue. Re-test for whatever the event was likely to introduce.
- Pump or pressure tank replacement. Anything that opens the well to surface contamination during service. Re-test for total coliform after the work is finished and the well has run for at least 24 hours.
- Well repair, casing work, or new construction near the well. Same logic — surface contamination can enter during disturbance. Coliform plus the core panel after work is complete.
- A flood event that submerged the wellhead or any part of the system. Almost always a coliform and nitrate trigger. The EPA and CDC both recommend not drinking the water without testing first.
- Unexplained illness in the household. Particularly gastrointestinal illness with no obvious cause that affects multiple household members. Run the microbiological panel even if the annual test was clean.
- Any change in taste, color, or smell. A sudden metallic taste, sulfur smell (rotten egg), brown or cloudy appearance, or unfamiliar odor. These changes are sometimes harmless and sometimes the first sign of a real problem — testing is how you tell which.
How to test — three options
Option 1: State-certified lab via your county health department or state environmental agency. This is the gold standard and the right default for the annual panel. State certification means the lab uses EPA-approved analytical methods under documented quality-control protocols. Many state programs bundle the core panel — coliform, nitrate, pH, TDS, arsenic — at subsidized rates for residents, sometimes free during specific awareness months. Start at your state department of environmental quality or department of health website; most have a "private well testing" page with the recommended provider list.
Option 2: State extension service or agricultural lab. Often the cheapest route for nitrate and coliform specifically. State agricultural extension services (typically run by land-grant universities) frequently offer well testing as a public-service function, and during planting and harvest seasons many run subsidized nitrate clinics. Less broad than a state-certified lab — usually limited to the core agricultural-relevant tests — but the price is hard to beat.
Option 3: DIY test strips and home kits. Useful as a screening tool between annual tests, not as a substitute for them. A $20 ten-strip kit can tell you in ten minutes whether your nitrate, pH, hardness, chlorine, and bacteria are in the rough vicinity of normal. The CDC notes that strip kits give useful directional answers but lose sensitivity at low concentrations — particularly for lead and arsenic. The right use of a home kit is between annual lab tests, to spot a sudden change worth investigating. Confirm any positive result with a state-certified lab before making treatment decisions.
Reading the results
Lab reports list each contaminant, your detected concentration, and the relevant comparison value — usually the EPA MCL. The MCLs for public water systems are not legally binding on private well owners, but they are the right reference because they represent the negotiated balance between health risk and treatment achievability. Numbers worth memorizing from the federal primary drinking water regulations:
- Total coliform: zero. Any detection is a boil-water situation. Re-test after shock chlorination.
- E. coli: zero. Same standard — any detection is a treatment trigger. Do not drink without boiling or alternative source.
- Nitrate: 10 mg/L as nitrogen. Above this, the water is unsafe for infants under six months. Stop using for formula immediately. Boiling does not help — it concentrates nitrate.
- Arsenic: 10 ppb. Above this, treatment is recommended. Some states (New Hampshire, New Jersey) have set state-level limits at 5 ppb.
- Lead: 15 ppb action level. Above this, treatment is required for utilities; for private wells, the same number is the action threshold. The CDC has stated no safe blood lead level in children has been identified, so any detectable lead in pre-1986 housing is worth filtering.
- pH: 6.5 to 8.5. Below 6.5, water is acidic enough to leach copper and lead from interior plumbing. Above 8.5, taste and scaling issues appear.
A clean panel — zero coliform, nitrate well below 10 mg/L, arsenic below detection — is the expected result for most wells in low-risk geological zones. An exceedance is the headline that should drive your next decision.
Treatment after positive results
The right treatment depends on the contaminant. Same logic that applies to public water with detected contaminants applies to wells, just without the utility doing the work.
- Coliform or E. coli detected. Shock chlorination of the well is the standard first response, followed by re-testing 7 to 14 days later. If the contamination recurs, persistent treatment options include UV sterilization at point-of-entry or chlorination with carbon post-filtration. UV is the cleanest because it does not add chemicals to the water.
- Nitrate above 10 mg/L. Reverse osmosis at point-of-use is the standard consumer-grade fix — an AquaTru countertop unit or a Hydroviv under-sink system with a regional cartridge tuned to nitrate handles typical concentrations. For higher concentrations or whole-house treatment, anion exchange resin specifically charged with chloride is the standard professional answer.
- Arsenic above 10 ppb. Reverse osmosis (NSF/ANSI 58 with arsenic listed as a tested claim) at point-of-use, or iron-oxide adsorption media at point-of-entry. Standard activated carbon does not work — see the arsenic deep dive for the full mechanism story. The Big Berkey base elements are not certified for arsenic; the brand sells optional fluoride/arsenic add-on cartridges (PF-series) that bolt onto the base filters and add the activated alumina chemistry that handles arsenic. Configuration matters.
- PFAS detected at any level. Activated carbon (granular activated carbon or carbon block) at point-of-use, or reverse osmosis. Both technologies have NSF/ANSI 53 PFAS-specific certifications. For broader filter mechanism context, see RO vs Carbon vs Gravity.
- Lead above detection. NSF/ANSI 53 certified filter for lead reduction at the kitchen tap, plus a hard look at whether your interior plumbing has lead service lines, lead solder, or older brass fixtures that need physical replacement. Filtering is a stopgap; replacing the lead source is the durable fix.
Documentation
Keep dated test results in a folder. Paper, scanned PDF, or a labeled cloud folder — pick one. Three reasons:
Home insurance and liability. A documented test history establishes the baseline if a contamination event later raises an insurance claim. Without prior data, the burden of proving the contamination is recent rather than chronic falls entirely on you.
Real estate disclosure. Many states require well-water test results at property transfer — typically coliform and nitrate at minimum, sometimes a fuller panel. Buyers' agents increasingly request multi-year test history. Having three years of clean reports makes for a smoother sale.
Identifying drift. A single high arsenic reading in isolation is harder to interpret than three years of trend data showing arsenic creeping from 6 ppb to 8 ppb to 11 ppb. Year-over-year comparison is what catches the slow problems before they become acute. Photograph or scan the lab report; the paper copies fade.
TL;DR — the annual checklist
Every year, on a date you will remember:
- Core panel through a state-certified lab. Total coliform, E. coli, nitrate, pH, TDS, arsenic. Roughly $30 to $80.
- Region-specific add-ons on a two-to-three-year cycle. Pesticides (agricultural areas), radon (Northeast, Appalachia, mountain West), lead (pre-1986 housing), PFAS (military, airport, industrial proximity), iron and manganese (taste and staining).
- Whenever a trigger event occurs. Pump replacement, well repair, contamination event in the area, flood, septic failure, unexplained illness, sudden change in taste/color/smell — re-test immediately, do not wait for the annual cycle.
- Document everything. Dated lab reports in a folder. Helpful for insurance, real estate disclosure, and catching slow drift.
- Match treatment to contaminant. Coliform → shock chlorinate or UV. Nitrate → RO or anion exchange. Arsenic → RO or iron-oxide media. PFAS → activated carbon or RO. Lead → NSF/ANSI 53 filter plus interior-plumbing investigation.
For the public-water counterpart on reading utility reports, see How to Read Your Consumer Confidence Report. For the contaminant-specific deep dives, see Arsenic in Drinking Water and Nitrates in Drinking Water. For broader testing context across both private and public sources, see How to Test Your Tap Water at Home.
