Well Water Testing: What to Test For, How and How Often

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If your home draws water from a private well, nobody else is testing it for you. Public water systems are regulated under the federal Safe Drinking Water Act and must monitor for dozens of contaminants. Private wells are not covered by those federal rules, so the responsibility for water quality falls on the owner. Regular well water testing is the only way to know whether the water is safe to drink, and it is the starting point for choosing any treatment equipment. This guide covers what to test for, how often, how to collect a sample, the difference between certified labs and home kits, how to read results against EPA drinking water standards and the basics of treatment. It summarizes EPA and CDC guidance current as of 2026; consult your physician about health symptoms and a certified laboratory or your local health department about testing decisions.

Part of our Plumbing & Water guide — start there for the full picture →

Well Water Testing: The Short Answer

Well water testing means sending samples of your water to a laboratory, or occasionally using a field test, to measure bacteria, chemicals and physical properties. At a minimum, the EPA and CDC recommend testing a private well at least once a year for total coliform bacteria, and many health agencies add nitrate, pH and total dissolved solids to that annual list. Beyond the annual basics, a broader one-time panel is worth running when you buy a home with a well, after drilling a new well, and every few years thereafter, covering metals such as arsenic and naturally occurring radioactive elements like uranium and radon where local geology makes them a concern.

Test sooner than your annual schedule if the water’s taste, color or smell changes, after flooding near the wellhead, after repairs to the well or plumbing, if someone in the household is pregnant or has an infant, or if a neighbor’s well has a known problem.

For buyers specifically, testing is one part of a broader well evaluation. The well inspection cost guide covers the purchase-focused side, including flow testing and equipment checks. This guide focuses on water quality itself, which owners need to keep monitoring long after closing.

What to Test For in Well Water

Total Coliform and E. coli

Coliform bacteria are a group of organisms common in soil and surface water. Most are not harmful themselves, but their presence signals that surface water, animal waste or septic effluent may be reaching the well. Labs usually report total coliform as present or absent, and if present, test further for E. coli, which indicates fecal contamination and can cause serious illness. A positive E. coli result means the water should not be consumed without boiling or an alternative supply until the well is disinfected and retested.

Nitrate and Nitrite

Nitrate enters groundwater from fertilizers, livestock, septic systems and naturally occurring sources. The EPA’s maximum contaminant level for public systems is 10 milligrams per liter (as nitrogen). High nitrate is particularly dangerous for infants under six months, because it can interfere with the blood’s ability to carry oxygen. Homes near agriculture or with a septic drain field upslope of the well should test for nitrate regularly.

pH, Hardness and Total Dissolved Solids

These are aesthetic and operational measures more than health measures, but they matter. Low-pH (acidic) water can corrode copper pipes and brass fittings, raising lead and copper levels at the tap. EPA’s secondary guidance suggests a pH range of 6.5 to 8.5. Hard water, high in calcium and magnesium, leaves scale on fixtures and water heaters. Total dissolved solids give a rough sense of mineral content and taste. Results for these parameters guide treatment choices such as neutralizers or softeners.

Arsenic

Arsenic occurs naturally in some rock formations and can dissolve into groundwater. The federal standard for public systems is 10 micrograms per liter (0.010 mg/L). Long-term exposure is linked to skin problems and several types of cancer. Arsenic has no taste or smell, so testing is the only way to detect it.

Uranium and Other Radionuclides

Uranium, radium and gross alpha radiation come from natural deposits in granite and other bedrock. EPA’s radionuclides rule sets limits for public water systems, including 30 micrograms per liter for uranium and 15 picocuries per liter for gross alpha. Parts of Colorado, including areas along the Front Range foothills, have geology where these elements can show up in well water. A one-time radionuclide panel is a reasonable precaution, with follow-up testing if results are elevated.

Radon in Water

Radon is a radioactive gas produced by uranium decay. It can dissolve into groundwater and is released into indoor air when water is used for showering, laundry and dishwashing. Most radon exposure in homes comes from soil gas, but in some private wells waterborne radon adds a measurable share. There is currently no final federal enforceable standard for radon in drinking water. If you are on a well in a radon-prone area, the guide to testing for radon in well water covers sampling, which requires special handling to avoid losing the gas, and the separate article on radon water tests explains how labs report results.

Other Contaminants to Consider

Depending on location and land use, other tests may be appropriate: lead and copper (especially in older homes), iron and manganese (staining and taste), sulfate, fluoride, volatile organic compounds near fuel storage or industrial sites, pesticides near farmland, and PFAS in areas with known contamination. The EPA’s list of potential well water contaminants is a useful checklist, and your local health department may know about problems specific to your area.

How Often Should You Test a Private Well?

These intervals reflect general EPA and CDC guidance. Local health departments sometimes recommend additional tests based on regional geology or known contamination.

How to Collect a Well Water Sample

Sampling errors are a common reason for false positives, particularly for bacteria. Most certified labs provide sterile bottles and written instructions; follow them exactly. General steps include:

1. Get the right containers. Bacteria samples need sterile bottles, often containing a preservative tablet. Do not rinse them out.
2. Choose the tap. Use a cold-water faucet without an aerator, ideally one that is not after a softener or filter, unless you are deliberately testing treated water.
3. Remove aerators and disinfect. Take off any aerator or screen and, if instructed, wipe or flame the faucet tip.
4. Run the water. Let cold water run several minutes to flush the plumbing and draw fresh water from the well. Some metals tests, especially lead, call for a “first draw” sample instead; follow the lab’s protocol.
5. Fill without touching. Avoid touching the inside of the cap or bottle. Fill to the marked line.
6. Keep it cold and ship fast. Bacteria samples typically need to reach the lab within a short holding time, often 24 to 30 hours, so collect them early in the week and avoid weekends and holidays.

Radon samples require special technique, usually filling a vial underwater or without any air bubbles, and very quick shipping because radon decays. Follow kit instructions precisely.

Certified Labs vs DIY Test Kits

Home test strips and kits are widely sold and can be helpful for quick checks of hardness, pH, chlorine or iron. Their limits are significant, though. Many kits are less accurate than laboratory analysis, do not test for metals or radionuclides at meaningful detection levels, and are not acceptable for real estate transactions or lender requirements.

A laboratory certified for drinking water analysis uses standardized methods, quality controls and documented chain of custody. In Colorado, state and local health agencies can point residents to certified labs, and many county health departments offer testing kits or discounted analysis. Ask the lab for a package designed for private wells, and confirm which tests are included before you order.

As a rough guide, a basic bacteria test often runs in the range of $25 to $75, a standard homeowner panel with bacteria, nitrate and common minerals may cost around $100 to $250, and comprehensive panels with metals, radionuclides and radon can exceed $300 to $500. Prices vary by lab and location, so compare packages rather than single tests.

Interpreting Your Results

Lab reports list each parameter, the measured value, units and often a reference limit. Because private wells are not federally regulated, those reference limits usually come from EPA standards for public water systems. They are a sensible benchmark, not a legal requirement for your well.

• Primary standards (MCLs) are health-based enforceable limits for public systems. Results above an MCL, such as nitrate above 10 mg/L or arsenic above 10 µg/L, are a reason to stop drinking the water or install treatment.
• Secondary standards cover taste, odor, color and corrosivity, such as pH, iron, manganese and total dissolved solids. They are guidelines rather than health limits, but exceedances often explain staining, odors or pipe corrosion.
• Bacteria results are typically reported as present or absent. Any total coliform presence is worth acting on; E. coli presence is urgent.
• Units matter. Watch for mg/L versus µg/L, and pCi/L for radiological results. A value that looks low may be in larger units than you expected.

If results are close to a limit, retest to confirm before investing in treatment. If they are well above a health-based limit, contact your local health department for guidance and consider an alternative drinking water source in the meantime.

Treatment Basics for Private Wells

Treatment should be matched to verified test results. No single device removes everything.

• Bacteria: shock chlorination can disinfect a contaminated well, but if bacteria return, the source needs to be found and fixed. Ultraviolet disinfection or continuous chlorination provide ongoing protection.
• Nitrate: reverse osmosis or ion exchange systems designed for nitrate removal, plus addressing the source.
• Arsenic and uranium: reverse osmosis, specialized adsorptive media or ion exchange, depending on chemistry.
• Radon in water: aeration systems or granular activated carbon, chosen based on concentration.
• Hardness and iron: water softeners and iron filters.
• Low pH: neutralizing filters to protect plumbing.

Look for treatment equipment certified to recognized performance standards for the specific contaminant, and retest after installation to confirm it works. Equipment needs maintenance, including filter changes, media replacement and UV lamp replacement, to keep performing.

Warning Signs Between Scheduled Tests

Many serious contaminants, including bacteria, nitrate, arsenic and radon, have no taste, color or smell. That is why scheduled testing matters. Still, some changes in the water or around the well are worth treating as prompts to test right away rather than waiting for the next annual sample:

• Cloudy or discolored water, or sediment in the first draw from a tap.
• A sudden change in taste, such as a metallic, salty or chemical flavor.
• A rotten-egg odor, which often points to hydrogen sulfide or sulfate-reducing bacteria.
• Red, brown or black staining on fixtures and laundry, usually iron or manganese.
• Blue-green staining, which can signal corrosive water dissolving copper plumbing.
• Gastrointestinal illness in the household or among guests with no other obvious cause.
• Flooding, heavy runoff or ponding near the wellhead, or damage to the well cap.
• New construction, septic work, fuel spills or fertilizer application nearby.

None of these signs identifies a contaminant on its own. They tell you which tests to prioritize, and a lab result tells you what is actually present.

Colorado and Front Range Considerations

Private wells are common across unincorporated parts of Elbert, Douglas, El Paso, Jefferson, Boulder and Adams counties, and in foothill and mountain communities west of the metro. Geology varies sharply over short distances. Wells drilled into fractured granite and metamorphic rock in the foothills can encounter naturally occurring uranium, radium and radon, while wells on the plains may be more exposed to nitrate from agriculture and septic systems. Because conditions can differ between neighboring properties, a neighbor’s clean result does not guarantee yours.

Colorado’s state health department and many county health agencies publish private well resources and can refer residents to certified laboratories. Some offer discounted testing programs. If you are unsure which tests make sense for your area, those agencies are a practical first call. Note also that well permits, construction records and water rights in Colorado are handled separately from water quality, so a properly permitted well can still have water that needs treatment.

What to Do If Bacteria Show Up

A positive total coliform result is common enough that it should not cause panic, but it does need follow-up. The usual sequence is to switch to bottled or boiled water for drinking and cooking, inspect the wellhead for a loose cap, cracked casing or pooling water, and then disinfect the well through shock chlorination following health department or contractor guidance. After the chlorine has been flushed out, retest. If bacteria return, the problem is likely structural, such as a failed casing seal or a nearby contamination source, and a licensed well contractor should evaluate it. Continuous treatment such as UV disinfection is an option once the source has been addressed.

Protecting the Well Between Tests

The EPA’s private well guidance emphasizes prevention: keep the wellhead capped and above grade, slope the ground away from the casing, and keep fuel, chemicals, fertilizer and animal waste away from the well. Know where your septic tank and drain field sit relative to the well; properties on septic should treat the two systems as linked, and the septic tank inspection guide explains how that system is evaluated. Keep records of every test so you can spot trends over time.

For home buyers lining up water testing alongside other specialists, the home inspector hiring guide explains how specialty tests fit into the inspection period and how to coordinate them.

References

• Private Drinking Water Wells — U.S. Environmental Protection Agency
• Protect Your Home’s Water — U.S. Environmental Protection Agency
• Potential Well Water Contaminants and Their Impacts — U.S. Environmental Protection Agency
• National Primary Drinking Water Regulations — U.S. Environmental Protection Agency
• Secondary Drinking Water Standards: Guidance for Nuisance Chemicals — U.S. Environmental Protection Agency

Buying a home on a private well somewhere along the Front Range? We can help you connect with a local inspector who can coordinate water testing with the rest of your inspection. Get in touch here.