A well water report is useful only if you know what was tested, what the numbers mean, and what decision comes next. The goal is not to memorize chemistry. The goal is to identify which results are acceptable, which need confirmation, and which require action.
Start with this principle: private well owners are responsible for testing and maintaining their own water. EPA drinking water rules apply to public water systems, not most private wells, but EPA standards are still commonly used as health-based comparison points.
First, Check the Basics
Before reading individual results, confirm that the report answers these questions:
- Who collected the sample?
- Where was the sample taken?
- Was it raw well water or treated water?
- What date and time was it collected?
- What date and time did the lab receive it?
- Was the lab certified for the tests performed?
- Are the results marked final?
- Are any samples flagged as late, held too long, diluted, or otherwise qualified?
This matters most for bacteria. A total coliform result can be invalid or less useful if the sample was collected incorrectly, taken from the wrong location, or delivered late.
Understand the Units
Water reports commonly use:
| Unit | Meaning | Common examples |
|---|---|---|
| mg/L | milligrams per liter, roughly parts per million in water | nitrate, chloride, sulfate, hardness |
| ug/L | micrograms per liter, roughly parts per billion | arsenic, lead, some VOCs |
| pCi/L | picocuries per liter | radon, gross alpha, uranium-related radioactivity |
| MPN or CFU | estimated or counted bacteria concentration | total coliform, E. coli |
| SU | standard units | pH |
| umhos/cm or uS/cm | electrical conductivity | dissolved ions |
| presence/absence | detected or not detected | total coliform, E. coli |
Do not compare values until units match. A result of 0.010 mg/L is the same concentration as 10 ug/L.
Compare Results to the Right Benchmark
Lab reports may list:
- EPA Maximum Contaminant Levels, often called MCLs
- EPA Secondary Maximum Contaminant Levels for taste, odor, color, staining, or scaling
- State standards or advisory levels
- Lab reporting limits
- “Non-detect” or “ND” values
MCLs are enforceable for public water systems. Private wells usually are not regulated the same way, but MCLs are still useful health-based reference points for deciding whether to take action.
Secondary standards are different. They often address nuisance issues such as staining, taste, odor, or corrosivity. A secondary standard exceedance can still matter because corrosive or mineral-heavy water can damage plumbing and treatment equipment.
What “Non-Detect” Really Means
“ND” does not mean a contaminant is impossible to be present. It means the lab did not detect it above the reporting limit for that method.
Always look for the reporting limit. If a contaminant has a health benchmark of 5 ug/L but the lab reporting limit is 10 ug/L, the test may not be sensitive enough for your decision.
Core Well Water Results
Total Coliform
Total coliform is an indicator test. Coliform bacteria are common in soil, plants, surface water, and animal or human waste. A positive result does not prove which germ is present, but it does mean a pathway may exist for contamination to enter the well.
If total coliform is present, do not stop at “shock the well and move on.” Confirm whether E. coli was tested, inspect the well, review recent repairs or flooding, disinfect when appropriate, and retest.
See what to do if your well water tests positive for coliform for a step-by-step response.
E. coli or Fecal Coliform
E. coli or fecal coliform is more urgent than total coliform alone because it suggests fecal contamination. Use bottled water or another safe source for drinking, cooking, brushing teeth, and food preparation until local health guidance and follow-up testing indicate the water is acceptable.
Boiling can address many microbial risks in an emergency, but it does not remove nitrate, arsenic, lead, salts, fuel chemicals, or other chemical contaminants.
Nitrate
Nitrate is usually reported as either nitrate as nitrogen (NO3-N) or nitrate as nitrate (NO3). These are not the same units. EPA’s MCL for nitrate as nitrogen is 10 mg/L.
Nitrate is especially important for households with infants, pregnant people, or anyone advised by a clinician to avoid elevated nitrate. If nitrate is high, switch to a safe alternative water source for drinking and infant formula while confirming results and choosing treatment.
Common nitrate sources include fertilizer, septic systems, animal waste, and natural soil conditions.
pH
pH describes how acidic or basic water is. Low pH can make water corrosive, which can increase metals leaching from plumbing. High pH can contribute to scale and treatment issues.
pH is not a stand-alone safety verdict. Read it together with alkalinity, hardness, copper, lead, iron, and plumbing symptoms.
Total Dissolved Solids
Total dissolved solids, or TDS, estimates the amount of dissolved minerals and salts in water. High TDS can affect taste, scaling, and treatment selection, but it does not identify what is dissolved.
A TDS result cannot tell you whether arsenic, nitrate, lead, PFAS, pesticides, or bacteria are present.
Common Metals and Minerals
Arsenic
Arsenic is odorless and tasteless. It can occur naturally in groundwater and can also come from some agricultural or industrial sources. EPA’s arsenic standard for public drinking water is 10 ug/L, also written as 0.010 mg/L.
If arsenic is near or above the benchmark, confirm with a certified lab and choose treatment certified for arsenic reduction. Not every filter removes arsenic, and treatment choice can depend on whether arsenic is present as arsenic III or arsenic V.
Lead
Lead often comes from plumbing, fixtures, solder, or well components rather than the aquifer itself. Sampling method matters. A first-draw sample can show what water picked up while sitting in pipes, while a flushed sample may better represent the source water.
If lead is detected, consider both immediate exposure reduction and plumbing investigation. Use treatment devices certified for lead reduction only as directed, and replace cartridges on schedule.
Iron and Manganese
Iron and manganese commonly cause staining, metallic taste, black or orange particles, and treatment fouling. They are often nuisance contaminants, but manganese can also have health-based guidance depending on concentration and state.
Treatment depends on the form of the metal, pH, oxygen, and whether iron bacteria are involved. A softener may help some dissolved iron problems, but it is not a universal fix.
Hardness
Hardness is mainly calcium and magnesium. It affects scale, soap performance, water heater efficiency, and appliance life. It is usually reported as mg/L as calcium carbonate or grains per gallon.
Hardness treatment is a comfort and equipment decision unless another contaminant is also present.
Results That Need Local Context
Some contaminants require state or local guidance because risk varies by region:
- PFAS
- Uranium and radionuclides
- VOCs from fuel, solvents, or industrial sites
- Pesticides and herbicides
- Road salt indicators such as chloride and sodium
- Hydrogen sulfide, methane, and other gases
If your report shows any of these, contact your health department, state drinking water program, or extension office. Ask whether the result is common locally, whether resampling is recommended, and which treatment options have documented performance.
Read Raw and Treated Samples Separately
If you have a filter, softener, neutralizer, UV system, or reverse osmosis unit, confirm whether the sample was taken before or after treatment.
Raw water results help diagnose the well. Treated water results show what your household is actually drinking at that tap.
For treatment verification, test both:
- Raw water before treatment
- Treated water after the equipment
This helps distinguish a source-water problem from a treatment maintenance problem.
When to Retest
Retest when:
- Total coliform, E. coli, nitrate, arsenic, lead, or another health-related contaminant is detected above a benchmark
- A sample was mishandled or flagged by the lab
- Results do not match symptoms or nearby well data
- You disinfect, repair, or replace well components
- You install or service treatment equipment
- Flooding, construction, or land disturbance occurs near the well
- Taste, odor, color, or clarity changes
For routine maintenance, test at least annually for total coliform, nitrate, pH, and TDS. Add local contaminants as recommended.
What Not to Do
- Do not buy treatment based only on a sales demonstration.
- Do not assume clear water is safe.
- Do not ignore units.
- Do not compare nitrate as nitrogen to nitrate as nitrate without converting.
- Do not assume one good report protects you forever.
- Do not use a treatment device for a contaminant unless its certification and instructions support that claim.
A Simple Reading Workflow
- Confirm the sample location, date, and lab certification.
- Identify whether the sample is raw or treated water.
- Flag any positive bacteria results.
- Compare health-related chemicals to EPA or state benchmarks.
- Review nuisance results that affect plumbing and treatment.
- Check reporting limits for non-detect results.
- Decide whether to retest, repair, treat, or monitor.
- Keep the report with your well records.
Bottom Line
A well water report is a decision document. Read the collection details first, compare results using the correct units, and act on health-related contaminants before nuisance issues.
When a result is positive, high, unexpected, or tied to a vulnerable household member, confirm it with a certified lab and get local guidance before relying on treatment claims.