Start here: CDC recommends that private well owners test for nitrates at least once a year and use a state-certified laboratory. If a result is high, unclear, or close to a value mentioned by an agency, contact the lab and local health department before deciding what it means for your household. Federal drinking-water rules for public systems do not regulate privately owned wells.
When to test a private well for nitrate
Include nitrate in the annual well-water test. CDC also says to test after events such as flooding, a well repair, a known local water problem, or a change in the water. EPA notes that nitrate and nitrite levels are typically highest from April through July and recommends testing after floods that cover the well. Ask your local health department whether local conditions call for additional timing or tests.
Nitrate can reach groundwater from fertilizers, manure, septic systems, wastewater, and runoff, according to EPA’s private-well contaminant guidance. A water test is needed to know whether it is present; appearance, taste, and smell cannot establish a nitrate result.
Check the unit before comparing numbers
Laboratory reports may express nitrate as nitrogen (NO3-N, “nitrate-nitrogen,” or “as N”) or as the full nitrate ion (NO3, “as nitrate”). EPA’s public drinking-water limit of 10 mg/L is expressed as nitrogen; the equivalent is about 44 mg/L when expressed as nitrate. The unit label matters: 10 mg/L as nitrate is not the same concentration as 10 mg/L as nitrogen. EPA documents the nitrate-as-nitrogen basis and the corresponding value for nitrate-ion reporting.
EPA’s public-system value is a reference, not a private-well compliance determination. CDC explains that EPA public drinking-water rules do not apply to privately owned wells. State and local health departments can tell you which guidance applies where you live.
Convert the report unit
Use this only to convert between the two reporting units. It does not assess whether water is safe or replace the lab’s interpretation.
Conversion factor: 1 mg/L as nitrogen ≈ 4.43 mg/L as nitrate. Confirm the analyte and unit with your laboratory if the report label is unclear.
Questions to ask about your result
- Is the result reported as NO3-N or as NO3? What is the unit?
- What method, reporting limit, and comparison value appear on this report?
- Does the comparison value apply to a public water system, a private well recommendation, or another purpose?
- Does the lab or local health department recommend a confirmation sample or other tests for this location?
- When should the well be tested again, and what water source should the household use while the result is being reviewed?
Do not compare readings from different units until the lab confirms the basis. Our well-water report guide explains other report fields and questions to ask.
If a result is high or uncertain
Contact the laboratory that ran the test and your local health or environmental department. Ask them to interpret the result using the report’s exact unit and applicable state or local guidance. CDC recommends contacting the local health department when well-water results show harmful chemicals; the department can explain next steps.
Do not boil water to remove nitrate. Boiling can kill germs, but CDC says it does not remove chemical contaminants. Use a known safe alternative source while you get advice about a high or uncertain nitrate result; do not assume boiling has made the water safe.
EPA advises not to use well water above its stated nitrate value—or water whose safety is uncertain—to prepare infant formula or food, and to use an alternate water source while getting local guidance. Because reports can use different nitrate units, confirm the unit with the lab promptly if an infant may drink the water. Seek health advice from a clinician or public-health agency for individual concerns.
Do not choose a filter from the number alone
If treatment is considered, ask the local health department or a qualified water professional about options for the confirmed contaminant and the exact test result. Check that a treatment system has an independently verified claim for nitrate reduction, follow its maintenance instructions, and retest the water after installation to confirm the treatment is working. No single home treatment type addresses every water-quality issue.
Primary sources
- CDC: Guidelines for Testing Well Water — annual tests, when to test sooner, and where to get help interpreting results.
- CDC: Guidelines for Treating Well Water — use an alternate safe water source for chemical contamination; boiling does not remove chemicals.
- U.S. EPA: Private Wells and Drinking Water Safety and Infants — nitrate precautions, seasonal testing notes, flooding, and local guidance.
- U.S. EPA: National Primary Drinking Water Regulations — current public-system MCL listed as 10 mg/L measured as nitrogen.
- U.S. EPA: Contaminant Occurrence Support Document, nitrate chapter — equivalent nitrate reporting value (about 44 mg/L as NO3).
- U.S. EPA: Potential Well Water Contaminants and Their Impacts — common nitrate sources and private-well context.
This guide explains general testing and report terminology. It does not interpret an individual result, diagnose health risk, or recommend treatment for a specific home. Follow the laboratory’s instructions and your state or local health department’s guidance.