The short answer: nearly every private well should be tested for total coliform bacteria and E. coli, nitrate, and, once, arsenic and lead. That short list covers the contaminants that are both common and genuinely harmful. Everything beyond it, from radon to pesticides, is worth adding only when your local geology or land use makes it plausible.
Testing for everything is expensive and mostly wasted. Testing for the right handful is affordable and actually protective.
When people finally decide to test their well, the usual mistake is one of two extremes: pay a lab several hundred dollars for a giant panel that includes contaminants irrelevant to their region, or test only for whatever the driller happened to check years ago and miss the arsenic sitting in their bedrock. The useful middle is a short, prioritized panel built on two questions: what is common everywhere, and what is common here.
The core panel: test these on almost any well
These contaminants are common across the country and serious enough that they belong on essentially every well's test list.
| Test | Why it matters | EPA limit |
|---|---|---|
| Total coliform & E. coli | Indicates surface water and possible pathogens reaching the well | Zero (no coliform detected) |
| Nitrate | Dangerous to infants under six months; tracks farming and septic activity | 10 mg/L (as nitrogen) |
| Arsenic | Naturally occurring in some bedrock; linked to cancer at low levels | 10 ppb (0.010 mg/L) |
| Lead | Usually from older well and plumbing components; harmful to children | 15 ppb action level |
| pH & hardness | Not a health risk, but low pH can leach lead and copper from pipes | Secondary (aesthetic) standards |
Coliform and nitrate are the annual tests (see how often to test). Arsenic and lead only need to be checked periodically, since they change slowly, but they should be checked at least once because you cannot detect them by taste, smell, or appearance.
The local panel: add these based on where your well is
The rest of what a lab could test for is not worth paying for blindly. It becomes worth testing when something about your location makes it plausible. A few common examples:
- Radon in water is worth testing where wells draw from granitic bedrock, the same terrain that produces high soil-gas radon. It is a separate exposure pathway from radon in the air.
- Pesticides and herbicides become relevant near intensively farmed land, especially combined with a shallow well.
- Fluoride occurs naturally in some aquifers and has both a health limit and a lower cosmetic guideline.
- Sulfate, iron, and manganese are mostly nuisance issues (taste, staining, odor) but manganese has a health advisory relevant to infants.
- Volatile organic compounds matter near fuel stations, dry cleaners, or a known spill.
- PFAS may be worth testing near industrial sites, airports, or firefighting-foam use, where the EPA has set enforceable limits for several of these compounds.
How to decide what to add without guessing
The contaminants in your groundwater are not random. They track the aquifer your well draws through and the land use around it. The USGS domestic-wells program has sampled tens of thousands of private wells and published which contaminants exceed health benchmarks by region and aquifer, which is the evidence base for deciding what is plausible near you. Our report turns that data into a ranked panel for your specific address.
How to read the "limit" once you have a result
Every number on your lab report should be compared to the EPA's benchmark for that contaminant. The EPA sets Maximum Contaminant Levels (MCLs), which are legally enforceable for public water systems, for contaminants such as nitrate, arsenic, and lead. For aesthetic issues like hardness, iron, and pH, the EPA publishes Secondary Maximum Contaminant Levels, which are guidelines rather than health limits. Knowing which kind of limit you are looking at tells you whether a high number is a health decision or just a plumbing annoyance.
One important honesty note: a private well has no legal obligation to meet any of these. The MCL is still the right yardstick because it is the level a public utility must not exceed, but exceeding it on your well means you decide what to do, not a regulator.
Use a certified lab, and collect the sample correctly
Test through a laboratory certified by your state for drinking water, or through your county or state health department. The lab provides sample bottles and instructions. Collection technique matters most for bacteria: touching the inside of the bottle or the tap can introduce coliform and produce a false positive, so follow the lab's steps exactly.
Sources
- US Environmental Protection Agency. National Primary Drinking Water Regulations. MCLs including arsenic (0.010 mg/L), nitrate (10 mg/L as N), and the lead action level (15 ppb). epa.gov.
- US Environmental Protection Agency. Secondary Drinking Water Standards. Aesthetic guidelines for pH, hardness, iron, manganese, and sulfate. epa.gov.
- US Geological Survey. Domestic (Private) Well Water Quality. National sampling of private wells and contaminant occurrence by aquifer and region. usgs.gov.
- US Environmental Protection Agency. Private Drinking Water Wells. Guidance on selecting tests and using certified laboratories. epa.gov/privatewells.
Related guides
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