Well Water Testing: What to Test and How Often
Water testing for a well comes down to one rule: test at least once a year for total coliform bacteria, nitrates, total dissolved solids and pH, using a state-certified lab. Test again any time something changes, like a flood, a well repair, a new baby or water that suddenly tastes, looks or smells different. Nobody else will do it for you, because private wells aren't regulated the way city water is.
What to test every year
The CDC's annual list:
| Test | Why it matters |
|---|---|
| Total coliform bacteria | Coliforms aren't a threat themselves, but they signal that harmful bacteria may be getting in |
| Nitrate | Dangerous to infants under six months above EPA's limit |
| Total dissolved solids (TDS) | A general measure of what's dissolved in the water; a jump means something changed |
| pH | Low pH water corrodes pipes and can pull metals out of plumbing |
Most labs sell a homeowner package that covers these. If the coliform test is positive, the lab will usually run E. coli on the same sample, which tells you whether the contamination is fecal.
Tests to add, depending on your well
The annual list is the minimum. Ask your county or state health department what's common in your area's groundwater; depending on where you live, that can include arsenic, uranium, fluoride, pesticides or other chemicals.
Add these if you've seen the problem:
- Iron, manganese, hardness and pH if you have stains, scale or a metallic taste. These decide which treatment works. See iron and manganese.
- Hydrogen sulfide and sulfate if the water smells like rotten eggs. Penn State says hydrogen sulfide must be tested in the home or the sample chemically stabilized, so ask the lab first. See rotten egg smell in well water.
- Turbidity and bacteria if the water clouds up after rain. See sediment and sand in well water.
How often to test, and when to test right away
At least once a year for the core tests. The CDC also says to check the well itself each spring for mechanical problems.
Test sooner when:
- you hear about well water problems in your area,
- the well floods, or land near it is disturbed (new construction, a nearby waste site),
- any part of the well system is repaired or replaced,
- the water's taste, color or smell changes,
- someone in the house becomes pregnant, or a child comes to live with you.
EPA adds that you may want to test more often if small children or older adults live in the house. Minnesota's health department says to test nitrate before bringing a new baby home.
A good habit is to test on the same week every year, like the week you change the furnace filter. Results from the same season are easier to compare.
How to take a clean sample
The sample is where most bad results come from. A dirty faucet or a rinsed bottle gives you a false positive, and you spend money chlorinating a well that was fine.
- Get the bottles from the lab. Use the containers and instructions the lab sends. Bacteria bottles are sterile and often contain a preservative, so don't rinse them.
- Pick the right tap. Use a cold tap without a swivel spout, a hose attachment or a filter on it. Pull the aerator off.
- Clean the faucet. Wipe the spout and let the water run before you fill the bottle, for as long as the lab instructions say.
- Don't touch the inside of the cap or bottle, and don't set the cap down face-first on the counter.
- Get it to the lab fast. Bacteria samples have a short time limit. Collect on a day the lab accepts samples, keep it cold and ship or drop it off the same day.
For iron and manganese, NDSU recommends sampling from a faucet at or near the well after running the water for 15 minutes. If you have metal pipes or a galvanized tank, send a second sample from inside the house too.
Where to send it, and lab vs home kit
Use a state-certified laboratory. Your county government or health department can give you a list, and EPA notes that some local health departments offer free private well testing.
Home test kits are fine for a quick screen, and a hardness strip is a useful way to check a softener. For anything that touches health, use a lab. UMass Extension warns that home test kits may not be accurate, and a bacteria or nitrate result is not the place to guess.
Reading your results
Compare each result with EPA's primary (health) and secondary (taste and staining) standards. Private wells aren't legally bound by them, but they're the best yardstick available.
| Contaminant | Standard | Type |
|---|---|---|
| Total coliform, E. coli | Any positive: call the health department, disinfect and retest | Health |
| Nitrate (as nitrogen) | 10 mg/L | Health |
| Nitrite (as nitrogen) | 1 mg/L | Health |
| pH | 6.5 to 8.5 | Secondary |
| Total dissolved solids | 500 mg/L | Secondary |
| Iron | 0.3 mg/L | Secondary |
| Manganese | 0.05 mg/L | Secondary |
| Sulfate | 250 mg/L | Secondary |
| Chloride | 250 mg/L | Secondary |
Hardness has no EPA standard; see how to test water hardness at home for how to read it.
What to do next
If anything is over a health standard, contact your health department and retest to confirm. EPA notes bacteria can often be controlled with disinfection such as chlorine, ozone or UV light, and the usual first step is a shock chlorination followed by a retest. Depending on the contaminant and the well's condition, treatment may not be enough and a new well or water source may be needed.
- Bacteria: coliform bacteria in well water and shock chlorinating a well
- Nitrate: nitrates in well water
- Repeated bad results: have a contractor check the cap, casing and seal with a well inspection
FAQ
How do I test my well water?
Order a bottle kit from a state-certified lab, follow its sampling instructions exactly, and return the sample within the lab's time limit. At minimum, test for total coliform, nitrate, TDS and pH every year.
Where can I get my well water tested for free?
Start with your county or state health department. EPA says some local health departments offer free private well testing. If yours doesn't, they can give you a list of certified labs.
How often should well water be tested?
At least once a year for the core tests. Test again after flooding, well repairs or any change in taste, color or smell, and when someone in the house is pregnant or a new baby arrives.
Can I test well water at home?
You can screen it with home kits, which are handy for hardness, pH and checking a softener. For bacteria, nitrate and anything else that affects health, use a lab, because home kits may not be accurate.
How do I test a well pump?
That's a different job from testing the water. Start with pressure readings and the pump's cycle pattern; our guide to signs of a bad well pump walks through it.
Sources
- Centers for Disease Control and PreventionGuidelines for Testing Well Water (opens in a new tab)
- U.S. Environmental Protection AgencyProtect Your Home's Water (opens in a new tab)
- U.S. Environmental Protection AgencyNational Primary Drinking Water Regulations (opens in a new tab)
- U.S. EPA via eCFR40 CFR Part 143, Secondary Drinking Water Regulations (143.3) (opens in a new tab)
- Minnesota Department of HealthNitrate in Drinking Water (opens in a new tab)
- NDSU ExtensionIron and Manganese Removal (opens in a new tab)
- UMass Amherst Center for Agriculture, Food, and the EnvironmentIron & Manganese in Private Drinking Water Wells (opens in a new tab)
- Penn State ExtensionHydrogen Sulfide (Rotten Egg Odor) in Water Wells (opens in a new tab)