Quick answer: Test a private well at least once a year for four things: total coliform bacteria, nitrate, pH and total dissolved solids (TDS). That is the baseline recommended by both the CDC and the EPA. Test more often, and for more contaminants, if something changes: flooding, repairs to the well, a new smell or color, a pregnancy, or a baby in the home. Always use a state-certified laboratory.
Unlike city water, nobody tests a private well for you. In the U.S., the owner is responsible for making sure the water is safe, and many contaminants have no taste, smell or color.
The four annual tests
| Test | What it tells you | Why it matters |
|---|---|---|
| Total coliform bacteria | Whether surface water or other contamination is getting into the well | Coliform should not be in groundwater. A positive result is a warning sign; E. coli means fecal contamination. |
| Nitrate | Fertilizer, manure or septic influence | High nitrate is dangerous for babies under 6 months. The limit is 10 mg/L as nitrate-nitrogen. |
| pH | How acidic or alkaline the water is | Low pH water can corrode pipes and pull metals such as copper and lead into the water. |
| Total dissolved solids (TDS) | The total amount of dissolved minerals | High or changing TDS can point to other problems and affects treatment choices. |
If a result comes back high, see our guides to coliform bacteria in well water and nitrate in well water.
When to test more often
The CDC recommends testing again, or testing for more contaminants, when:
- You hear about problems with well water in your area.
- There is flooding, land disturbance or a waste site near your well.
- You replace or repair any part of the well system (pump, pipes, pressure tank, cap).
- You notice a change in taste, color or smell.
- Someone in the home becomes pregnant.
- A child starts living with you.
The EPA adds that homes with small children, older adults, pregnant people or nursing mothers may want to test more often, because they are more sensitive to contaminants.
Tests that depend on where you live
Beyond the annual basics, what else to test for depends on local geology and land use. Your county or state health department can tell you which contaminants are common in your area. Typical add-ons:
| Test | Consider it if… |
|---|---|
| Arsenic | Your region has naturally occurring arsenic in groundwater |
| Lead and copper | Your home has older plumbing, or your water is acidic (low pH) |
| Radon | Radon is common in your area or was found in your indoor air |
| Iron and manganese | You see orange, brown or black staining (read more) |
| Hardness | You see scale on fixtures or are sizing a water softener |
| Hydrogen sulfide | The water smells like rotten eggs |
| Pesticides or VOCs | The well is near farm fields, fuel tanks or industrial sites |
How to get your well water tested
- Find a state-certified lab. Your local health or environmental department keeps a list. You can also call the EPA Safe Drinking Water Hotline at (800) 426-4791.
- Use the lab’s bottles and instructions. Bacteria samples in particular must be collected in a sterile bottle and reach the lab quickly, usually within about a day, so check the lab’s drop-off or shipping rules before you sample.
- Sample from a cold tap that does not go through a softener or filter, unless you are testing how well your treatment works.
- Keep your results. A record over the years shows whether anything is changing.
Home test strips are fine for a quick check of hardness or pH. For bacteria, nitrate and anything health-related, use a certified lab.
What to do with the results
- Everything within limits: retest next year.
- Bacteria present: stop drinking the water untreated (boil it or use bottled water) and follow our shock chlorination guide.
- Nitrate, arsenic or lead above the limit: do not use the water for infants or formula, contact your health department, and look at point-of-use treatment such as reverse osmosis.
- Nuisance problems (iron, hardness, smell): these affect taste, stains and plumbing more than health; see our treatment guides.
Frequently asked questions
How often should well water be tested?
At least once a year for coliform bacteria, nitrate, pH and TDS, and again after any event that could affect the well.
What time of year is best to test?
Spring, after snowmelt or heavy rain, is a common choice because surface contamination is more likely to show up then. The most important thing is to test at the same time each year so results are comparable.
Does a new well need testing?
Yes. Test a new well before you drink from it and after any work on the pump or plumbing.
Can I test for bacteria myself?
Home kits exist, but a state-certified lab is more reliable and its report is accepted for real estate transactions.
Related guides
- Coliform bacteria in well water: what a positive test means
- Nitrate in well water: safe levels and treatment
- Buying a home with a well: inspection checklist
Sources
- CDC – Guidelines for Testing Well Water
- U.S. EPA – Protect Your Home’s Water
- Penn State Extension – Nitrates in Drinking Water
This guide is for general information. Your state or county health department is the best source for contaminants of concern in your area.
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