If your household uses a private well, you are responsible for checking the water. Private wells are not routinely monitored under the federal Safe Drinking Water Act in the way public water systems are.
At least once each year, CDC recommends testing private well water for total coliform bacteria, nitrate, pH, and total dissolved solids. You may need additional tests based on local geology, nearby land use, the well's condition, and who drinks the water.
You should also test after flooding, well repairs, a change in taste or appearance, or a known contamination problem nearby.
The best testing plan is not the largest laboratory package. It is a targeted plan that combines:
- A small annual core panel
- Tests recommended for your location
- Extra tests triggered by events or household risk
- Correct sample collection by a state-certified laboratory's instructions
Why Private Well Water Needs Its Own Testing Plan
A public water utility treats and tests water according to regulatory requirements. It also provides customers with an annual water quality report.
A private well works differently. The well owner is usually responsible for maintenance, testing, and treatment. There may be state or local requirements when a well is constructed, a property is sold, or a particular problem occurs, but there is no single federal testing program for every private well.
Groundwater can contain substances from rocks and soil. It can also be affected by septic systems, fertilizers, animal waste, fuel, industrial chemicals, flooding, and poor well construction.
Contamination is not always obvious. Water can look, taste, and smell normal while containing germs, nitrate, arsenic, or other substances. A bad taste or odor can justify investigation, but normal sensory qualities do not prove that the water is safe.
The Annual Core Tests
CDC recommends testing at least once each year for four basic measures: total coliform bacteria, nitrate, pH, and total dissolved solids.
These tests do not detect every possible problem. Together, they provide a practical baseline and may reveal changes that need further investigation.
Total coliform bacteria
Total coliforms are a broad group of bacteria found in soil, vegetation, surface water, and the intestines of people and animals. Most total coliform bacteria are not harmful by themselves. Their presence can indicate that the well, cap, casing, plumbing, or surrounding ground has allowed contamination to enter.
A laboratory may also report fecal coliforms or Escherichia coli (E. coli). Detection of E. coli is stronger evidence that fecal contamination has reached the water.
A standard indicator test does not identify every disease-causing organism. It is used because testing individually for all possible pathogens would be impractical.
Nitrate
Nitrate can enter groundwater from fertilizers, septic systems, animal waste, wastewater, and natural sources. It is especially important for households with infants because high nitrate exposure can interfere with the blood's ability to carry oxygen.
Do not boil nitrate-contaminated water to make it safe. Boiling removes water as steam but does not remove nitrate, so it can increase the remaining concentration.
If a baby younger than 12 months lives in the home or infant formula is prepared with well water, ask the health department whether testing should be more frequent than once a year.
pH
pH describes how acidic or basic the water is. It is mainly an indicator rather than a stand-alone safety test.
Water with a low or high pH can corrode plumbing, affect taste, interfere with treatment, or increase the release of metals from pipes and fixtures. An unusual pH result may lead to testing for lead, copper, or other metals.
Total dissolved solids
Total dissolved solids, often abbreviated TDS, estimate the amount of dissolved material in the water. A high value can affect taste and cause scale or deposits. A changing value may signal a change in the water source or well conditions.
TDS does not identify which substances are present. A separate laboratory analysis is needed to measure individual contaminants.
Do Not Order the Same Extra Tests Everywhere
The additional tests that matter depend on the well and its surroundings. Local geology may increase the chance of arsenic, uranium, radium, radon, fluoride, iron, or manganese. Nearby farms may raise concern about nitrate, pesticides, and animal waste. Fuel storage, dry cleaning, landfills, or industrial activity can point to volatile organic compounds and other chemicals.
Start with your county or local health department, state environmental agency, cooperative extension service, or state geological survey. Ask which contaminants are documented in local groundwater and which tests they recommend for wells like yours.
Possible additional tests include:
Situation or local concern | Tests to discuss with a local authority or laboratory |
|---|---|
Arsenic-prone geology | Arsenic |
Granite or radionuclide-prone areas | Uranium, radium, radon, or gross alpha screening |
Acidic or corrosive water | Lead, copper, pH, alkalinity, and corrosivity indicators |
Nearby agriculture or heavy fertilizer use | Nitrate, pesticides, and bacteria |
Livestock, manure storage, or a nearby septic system | Coliform bacteria, E. coli, and nitrate |
Fuel tank, gasoline spill, landfill, dry cleaner, or industry | Location-specific volatile organic compounds or other chemicals |
Salty taste or road-salt concern | Chloride, sodium, conductivity, and TDS |
Staining, metallic taste, or scale | Iron, manganese, hardness, pH, and other locally relevant minerals |
PFAS investigation or known contamination nearby | Specific PFAS analysis recommended by the responsible agency |
This table is a starting point, not a universal test panel. Distance alone does not determine risk. Groundwater direction, well depth, soil and rock, well construction, and the type of contamination also matter.
When to Test Beyond the Annual Schedule
Do not wait for the next annual test when something has changed.
Arrange testing when:
- Floodwater reaches the well or the area around it
- The well cap, casing, pump, pressure system, or plumbing is repaired or replaced
- The well has been disinfected
- The water changes in color, clarity, taste, or odor
- Sediment suddenly appears
- Water pressure or well performance changes without a clear explanation
- A septic system fails or sewage is released nearby
- Fuel, pesticide, fertilizer, manure, or another chemical spills near the well
- A nearby property or agency reports groundwater contamination
- Someone in the household becomes pregnant
- An infant or young child begins living in the home
- Household members have recurring gastrointestinal illness with no identified cause
- A new treatment system is installed or an existing system is serviced
The event determines the tests. Flooding may call for microbial testing and additional chemicals depending on what the floodwater contacted. A fuel spill needs a different panel. A corroded fixture may require metals testing.
Ask the health department or laboratory before collecting a sample. Testing for every possible contaminant is expensive and still may not answer the right question.
What to Do After a Flood
Floodwater can carry sewage, animal waste, fuel, pesticides, and other contaminants. Do not use a flooded well for drinking, cooking, brushing teeth, making ice, or preparing infant formula until local authorities say it is safe.
Use bottled water or another safe source. Boiling can kill many germs, but it does not remove fuel, pesticides, metals, nitrate, or many other chemicals. If chemical contamination is possible, boiling is not an adequate solution.
Have the well inspected and follow local instructions for disinfection. CDC advises waiting at least 7 to 10 days after emergency well disinfection before sampling, after all chlorine has been flushed from the system. Your local authority may use a different schedule based on the incident, so follow its directions.
One negative sample may not close a complex contamination investigation. The health department may recommend repeat samples or additional chemical tests.
Choose a Certified Laboratory Before Collecting Water
Use a state-certified drinking-water laboratory. Certification can be specific to a contaminant or analytical method, so confirm that the laboratory is certified for each test you need.
Contact the laboratory before sampling. It should provide:
- The correct sterile or chemically prepared containers
- Instructions for choosing a faucet or sampling point
- Steps for removing or retaining an aerator
- Any required flushing or stagnation period
- The correct fill level
- Preservation and refrigeration instructions
- A holding time and delivery deadline
- Chain-of-custody paperwork when needed
EPA provides links to state certification programs and certified drinking-water laboratories. A local health department may also offer testing or recommend a laboratory.
Mail-order and home test kits vary widely. Some can screen for a narrow problem. They are not automatically equivalent to analysis by a certified laboratory. If a result will guide health decisions, property decisions, or treatment purchases, use a laboratory method appropriate for that purpose.
Our guide on what home water tests can tell you explains the difference between a screening result and a defensible laboratory measurement.
How to Collect a Useful Sample
The laboratory's instructions take priority over general advice. Different tests require different containers and collection methods.
For example, a bacteriological sample usually requires a sterile bottle. Touching the inside of the cap, bottle, or faucet outlet can contaminate it. A metals sample may require acid-preserved containers. A volatile-organic sample may need to be filled without air bubbles.
Before sampling:
- Tell the laboratory whether you want to test raw well water, treated water, or both.
- Identify the exact faucet or sampling port.
- Ask whether filters, softeners, aerators, or hoses should be bypassed or removed.
- Read all instructions before opening a container.
- Prepare a cooler if the sample must remain cold.
Record the date, time, location, recent rain or flooding, well repairs, treatment status, and anything unusual. Label each bottle exactly as instructed.
If you want to evaluate a treatment system, paired samples may be useful: one before treatment and one after treatment. Ask the laboratory or water professional to design the comparison. Do not assume a kitchen tap represents untreated groundwater if the water has already passed through a softener, filter, or disinfection unit.
How to Read the Laboratory Report
Start with five questions:
- What was measured?
- What unit was used?
- Was the substance detected?
- What was the laboratory's reporting limit?
- What health-based or regulatory comparison value is shown?
Private wells are not regulated under federal drinking-water rules, but public-water standards can provide useful health benchmarks. Your state may have additional standards or guidance specifically for private wells.
“Not detected” does not mean a substance is absolutely absent. It means the laboratory did not find it above the method's detection or reporting limit in that sample.
Some values, such as pH and TDS, are indicators rather than direct diagnoses. A change from your previous result can be important even when the current number does not exceed a listed benchmark.
Keep every report. Results collected over time create a baseline for your well. A clear trend can reveal a developing problem earlier than a single isolated test.
What to Do If a Result Is High or Positive
Do not choose treatment based only on a sales recommendation.
First:
- Contact the laboratory and local health or environmental department.
- Ask whether the result needs confirmation with a second sample.
- Use bottled water or another safe source if advised.
- Identify the likely source and inspect the well.
- Decide whether the source can be removed or repaired.
- Select treatment only after defining the contaminant, concentration, and required flow.
- Verify treatment with follow-up testing.
The response depends on the finding. A damaged cap may need repair. Microbial contamination may require correcting the source and disinfecting the well. A nearby chemical release may require agency involvement. Naturally occurring arsenic may require a treatment system designed and certified for arsenic reduction.
No single device removes every contaminant. A sediment filter does not disinfect water. A water softener is not a general contaminant-removal system. A carbon filter that improves taste may not remove nitrate, arsenic, or microorganisms.
Use our guide on how to choose a water filter to match the treatment claim to the test result. If lead is detected, see Lead in Drinking Water: How to Test and Reduce Exposure.
Test Treated Water Too
Treatment equipment needs maintenance and verification. A system can stop working because a cartridge is exhausted, media is depleted, a membrane is damaged, settings are wrong, or maintenance is overdue.
The follow-up schedule depends on the contaminant and device. Test after installation to confirm performance. Then follow the manufacturer's maintenance schedule and the testing frequency recommended by the health department or water professional.
For a health-related contaminant, do not use taste or appearance as proof that treatment still works.
Keep a Simple Well Record
Create one folder for:
- The well construction log
- Pump, casing, and repair records
- A sketch showing the well, septic system, fuel tanks, and drainage
- Laboratory reports
- Treatment specifications and certifications
- Cartridge and media replacement dates
- Flood, spill, and disinfection records
- Contact details for the laboratory, health department, and well contractor
A record makes future results easier to interpret. It also helps a buyer, contractor, or health official understand the well without starting from zero.
A Practical Testing Schedule
Use this as a starting framework, then adjust it with local advice.
Time | What to do |
|---|---|
Every spring | Inspect the well cap, casing, drainage, and surrounding area for damage or standing water |
At least once each year | Test total coliform bacteria, nitrate, pH, and TDS |
On a locally recommended schedule | Test for arsenic, radionuclides, fluoride, manganese, or other regional contaminants |
After flooding or suspected contamination | Stop using the water as directed, inspect, disinfect if appropriate, and test for event-specific contaminants |
After well or plumbing repair | Test for bacteria and any contaminants relevant to the work |
After installing treatment | Test treated water to confirm that the system works |
When water changes | Test based on the new color, taste, odor, sediment, or performance problem |
When household risk changes | Ask about additional or more frequent testing during pregnancy or when an infant or young child moves in |
The Bottom Line
For most private wells, begin with annual testing for total coliform bacteria, nitrate, pH, and total dissolved solids. Then add tests based on local geology, nearby activities, the condition of the well, and the people using the water.
Use a state-certified laboratory and follow its collection instructions exactly. Test again after flooding, repairs, a change in the water, or a local contamination warning.
The goal is not to buy the biggest test panel. It is to ask the right question, collect the right sample, and act on the result.
References
- Centers for Disease Control and Prevention. Guidelines for Testing Well Water.
- Centers for Disease Control and Prevention. Private Drinking Water and Public Health.
- Centers for Disease Control and Prevention. How to Disinfect Wells After an Emergency. Updated May 29, 2025.
- U.S. Environmental Protection Agency. Private Drinking Water Wells. Updated June 3, 2026.
- U.S. Environmental Protection Agency. Protect Your Home's Water. Updated February 26, 2026.
- U.S. Environmental Protection Agency. Potential Well Water Contaminants and Their Impacts. Updated July 6, 2026.
- U.S. Environmental Protection Agency. Contact Information for Certification Programs and Certified Laboratories for Drinking Water.
- U.S. Environmental Protection Agency. Natural Radionuclides in Private Wells. Updated March 23, 2026.
- U.S. Geological Survey. Arsenic and Drinking Water.