How Often to Test Private Well Water (and What For)

TL;DR: Test private well water at least once a year for total coliform bacteria and nitrates, and test every 1-3 years for a broader panel that includes pH, hardness, and local contaminants like arsenic or radon. Test immediately after any flooding, a change in taste or color, nearby construction, or well repairs. A basic bacteria-and-nitrate test costs $15-$50 through a county health department; a full panel from a certified lab runs $100-$300.

_Last reviewed: August 2026 · 7 min read_

If you're on a private well, no one is checking your water for you. The EPA regulates public water systems, but roughly 23 million U.S. households on private wells are responsible for their own testing, and a lot of owners simply don't know how often, or for what.

Okoniq Property Hub helps you log well test dates, results, and repair history in one place, so you're not digging through old paper receipts when a buyer or health inspector asks for records.

How often should you test private well water?

Test once a year, minimum, for total coliform bacteria and nitrates. The CDC and most state health departments recommend annual testing for these two because bacteria and nitrate levels can change fast, sometimes within weeks, depending on rainfall, septic system performance, and agricultural runoff nearby.

Beyond the annual basics, run a fuller panel every 3 years that checks pH, total dissolved solids, hardness, iron, and manganese. If you live near farmland, a gas station, or an old industrial site, add pesticides, VOCs, or petroleum compounds to that 3-year panel. Wells in parts of New England, the Rocky Mountains, and the upper Midwest should also test for radon and arsenic, since those occur naturally in the bedrock in specific regions.

Test outside the schedule any time something changes. A new odor, cloudiness, a metallic taste, a household member who's pregnant or has a compromised immune system, a nearby flood, new construction or excavation within 100 feet of the wellhead, or any well repair are all reasons to test right away rather than wait for your annual date.

What should you actually test for?

At minimum, test for total coliform bacteria and nitrate/nitrite every single year. Coliform bacteria indicate whether surface contamination, often from septic systems or animal waste, has reached your water. It's not usually itself dangerous, but its presence signals a pathway for something worse to get in. Nitrates matter most for infants under 6 months and pregnant women; levels above 10 mg/L (the EPA's maximum contaminant level) can cause "blue baby syndrome."

Beyond the annual pair, test based on your location and well history:

| Test | Why it matters | How often | |---|---|---| | Total coliform / E. coli | Detects septic or surface contamination | Every year | | Nitrate/nitrite | Fertilizer and septic runoff, infant risk | Every year | | pH, hardness, TDS | Affects pipes, appliances, taste | Every 3 years | | Arsenic, radon | Naturally occurring in some bedrock | Every 3-5 years, or once if your region is a known hot spot | | Lead, copper | Corrosion from old plumbing | Once, then every 3-5 years if pipes are pre-1986 | | Pesticides/VOCs | Near farms, gas stations, dry cleaners | Every 3 years if you're within a mile |

If your home still has pre-1986 plumbing, lead testing is worth pairing with the electrical safety checks covered in 2-prong vs 3-prong outlets: how to upgrade safely, since older homes often carry multiple outdated systems that need attention at once.

What do the test results actually mean?

A "clean" result means no detectable coliform bacteria and nitrate under 10 mg/L, but the specific numbers on your lab report matter more than a pass/fail label. Total coliform should read zero. Any positive result means retest immediately, and if E. coli specifically shows up, treat the water as unsafe to drink until you resolve the source and get two clean retests in a row.

Nitrate levels between 5 and 10 mg/L aren't an emergency but are worth watching, especially if your well is near cropland that gets fertilized seasonally, since levels tend to spike after spring applications. Hardness above 180 mg/L (about 10.5 grains per gallon) means you'll likely want a water softener to protect appliances and fixtures. High iron or manganese won't usually make you sick but will stain sinks, tubs, and laundry, and can clog well pumps over time if left untreated.

If your results show elevated levels near your water heater or under sinks, check for related plumbing issues covered in 5 reasons water pools under your water heater, since a slow leak can sometimes coincide with contamination if groundwater is finding its way into your system.

What triggers an off-schedule test?

Four situations mean you test now, not on your usual annual date: flooding, nearby construction, a change in your water's look/smell/taste, or any work done on the well itself. Flooding is the biggest one. If your well casing sat underwater or near standing water for more than a day, bacteria can enter through the cap or casing seams, even in wells that tested clean months earlier.

New construction, drilling, or excavation within 100 feet of your wellhead can also disturb soil layers and introduce contaminants that weren't there before. The same goes for a new septic system nearby, whether it's yours or a neighbor's. If you notice standing water or drainage issues near your wellhead after storms, look at 5 drainage jobs you're forgetting before rainy season hits, since poor grading around a well is one of the most common (and fixable) contamination pathways.

Any repair to the well pump, casing, or pressure tank is also a trigger. Technicians working inside the wellhead can introduce bacteria even when they're careful, so a bacteria retest 2-4 weeks after any well service is standard practice, not overkill.

FAQ

How much does a private well water test cost?

A basic bacteria and nitrate test through a county health department typically costs $15 to $50. A full lab panel covering metals, VOCs, and other contaminants runs $100 to $300 depending on how many parameters you include.

Where do I get my well water tested?

Most county or state health departments offer low-cost coliform and nitrate testing, and can point you to state-certified labs for broader panels. Look for a lab certified under your state's environmental or health department, not a big-box retail kit alone, since certified labs are needed for results banks or buyers will accept.

Can I use a home test kit instead of a lab?

Home kits are fine for a quick check but aren't accurate enough for legal, real estate, or health decisions. For anything that affects a sale, a mortgage, or a health concern, use a certified laboratory.

Do I need to test well water before selling a house?

Most mortgage lenders and many state real estate disclosure laws require a well water test, usually for bacteria and sometimes nitrates or arsenic, within 30 to 90 days of closing. Check your state's specific requirements, since they vary widely.

What if my well water tests positive for bacteria?

Shock-chlorinate the well following your state health department's protocol, wait the recommended time (usually 24-48 hours), flush the system, then retest. If two consecutive retests come back clean, the well is considered safe again; if bacteria persists, call a licensed well contractor to inspect the casing and cap for a physical entry point.

This is educational information, not medical or environmental testing advice. Call a licensed well contractor or your state health department if test results come back abnormal or you're unsure how to interpret them.