How the interpreter works
- Health tests (bacteria, nitrate, arsenic, lead, PFOA, PFOS) are compared with EPA's primary standards or the lead action level. Any result above them puts the public-health steps first.
- Nuisance tests (iron, manganese, pH, TDS, odor) are compared with EPA's secondary guidelines. Neither set is legally binding on a private well; extension services say to use them as guidelines.
- Units: nitrate as NO3 ÷ 4.43 = as nitrogen. µg/L ÷ 1,000 = mg/L. Hardness mg/L ÷ 17.1 = gpg.
- Lead: 0.015 mg/L until Oct 31, 2027, then 0.010 mg/L. Manganese above its 0.3 mg/L health advisory counts as a health result.
EPA numbers the tool uses
| Test | EPA number | Type | Source |
|---|---|---|---|
| Total coliform bacteria | MCLG zero (EPA primary) | Health (primary / action level) | U.S. EPA |
| E. coli | MCLG zero (EPA primary) | Health (primary / action level) | U.S. EPA |
| Nitrate (as N) | MCL 10 mg/L as nitrogen (EPA primary; MCLG 10) | Health (primary / action level) | U.S. EPA; Minnesota Department of Health |
| Arsenic | MCL 0.010 mg/L (10 µg/L), MCLG zero (EPA primary) | Health (primary / action level) | U.S. EPA |
| Lead | Action level 0.015 mg/L (15 µg/L), dropping to 0.010 mg/L on Nov 1, 2027; MCLG zero (EPA) | Health (primary / action level) | U.S. EPA; U.S. EPA |
| PFOA | MCL 4.0 ng/L (ppt), MCLG zero (EPA primary, 2024 rule) | Health (primary / action level) | U.S. EPA |
| PFOS | MCL 4.0 ng/L (ppt), MCLG zero (EPA primary, 2024 rule) | Health (primary / action level) | U.S. EPA |
| Iron | 0.3 mg/L (EPA secondary, not enforceable) | Nuisance (secondary) | U.S. EPA |
| Manganese | 0.05 mg/L (EPA secondary). EPA health advisory 0.3 mg/L, as cited by Penn State and Nebraska Extension | Nuisance (secondary) | U.S. EPA; Penn State Extension; Nebraska Extension |
| Hardness | No EPA standard. Penn State classes above 7.0 gpg (120 mg/L) as hard | No EPA number | Penn State Extension |
| pH | 6.5–8.5 (EPA secondary) | Nuisance (secondary) | U.S. EPA |
| Total dissolved solids (TDS) | 500 mg/L (EPA secondary) | Nuisance (secondary) | U.S. EPA |
| Hydrogen sulfide / rotten-egg odor | No numeric EPA limit; odor has a secondary limit of 3 TON | Nuisance (secondary) | U.S. EPA; Penn State Extension |
| Cloudy, sandy or gritty water | No federal number for sediment on the secondary list | Nuisance (secondary) | U.S. EPA; Virginia Cooperative Extension |
The treatment order
| Step | Device (only if a result calls for it) | Why it goes here | Source |
|---|---|---|---|
| 1 | Sediment filter | RO and UV need particles removed first; oxidized iron clogs softener resin. | Virginia Cooperative Extension; Penn State Extension |
| 2 | pH correction (neutralizer or soda ash) | Iron media and chlorine oxidation have pH floors. A neutralizer adds hardness, which the softener then removes. | Nebraska Extension; Virginia Cooperative Extension |
| 3 | Iron, manganese and hydrogen sulfide removal | Oxidized iron fouls softener resin, so it comes out before the softener. | Penn State Extension; Nebraska Extension |
| 4 | Water softener | Hard water fouls RO membranes; a softener is the pretreatment for some downstream units. | Virginia Cooperative Extension |
| 5 | Activated carbon | Removes residual chlorine after chlorination; also used for PFAS. Placement varies: Nebraska's example puts carbon before the softener. | Virginia Cooperative Extension; Nebraska Extension; U.S. EPA |
| 6 | UV disinfection, last | Cloudy water or sediment limits UV light, so UV is typically the last device. | Virginia Cooperative Extension |
| Tap | Point-of-use RO or filter at the drinking tap | Fed by the treated whole-house water; for contaminants that matter only in drinking and cooking water. | Virginia Cooperative Extension; Wisconsin DHS |
Worked example
Coliform present, E. coli absent, nitrate 3.1 mg/L as N, iron 2.5 mg/L, manganese 0.08 mg/L, hardness 257 mg/L, pH 6.3, TDS 320 mg/L. Health steps first: Total coliform bacteria detected. Then: Sediment filter → pH correction (neutralizer or soda ash) → Iron, manganese and hydrogen sulfide removal → Water softener → UV disinfection, last. The softener does not take the iron because pH 6.3 is not above 6.7 (Penn State).
What this tool does not cover
- Uranium, radium, pesticides, VOCs, nitrite, copper, tannins, and PFAS other than PFOA and PFOS.
- Home test strips: Nebraska Extension says kits "are not a substitute for certified laboratory analysis". See test kits vs a certified lab.
- Why the well is contaminated: ask a licensed well contractor.
Related
- Well water filtration system: choose by your test results
- Iron filter for well water
- Water softener size calculator
Frequently asked questions
What should my well water test results be?
EPA’s goal for total coliform and E. coli is zero; nitrate should not exceed 10 mg/L as nitrogen and arsenic 0.010 mg/L. Nuisance guidelines: 0.3 mg/L iron, 0.05 mg/L manganese, 500 mg/L TDS, pH 6.5–8.5.
What do I do if coliform bacteria is present in my well water?
Minnesota’s health department: use bottled, boiled or other safe water for drinking and cooking, disinfect the well (or have a licensed well contractor do it), and retest before normal use.
What is a normal nitrate level in well water?
EPA’s limit is 10 mg/L as nitrogen, about 44 mg/L if reported as NO3. Above that, do not give the water to babies under six months, and do not boil it: boiling concentrates nitrate.
Sources
- U.S. EPA, National Primary Drinking Water Regulations (table of MCLs, MCLGs and the lead action level) · checked October 5, 2026
- U.S. EPA, Secondary Drinking Water Standards: Guidance for Nuisance Chemicals · checked October 5, 2026
- U.S. EPA, Per- and Polyfluoroalkyl Substances (PFAS): Final PFAS National Primary Drinking Water Regulation (last updated 2026-05-18) · checked October 5, 2026
- U.S. EPA, Reducing PFAS in Your Drinking Water with a Home Filter (fact sheet, April 2024), pp.1-2 · checked October 5, 2026
- U.S. EPA, Basic Information about Lead in Drinking Water (updated 2026-06-18) · checked October 5, 2026
- U.S. EPA, Potential Well Water Contaminants and Their Impacts (updated 2026-07-06) · checked October 5, 2026
- CDC, Guidelines for Testing Well Water (last reviewed 2024-07-01) · checked October 5, 2026
- Minnesota Department of Health, Nitrate in Well Water (updated 2026-06-05) · checked October 5, 2026
- Minnesota Department of Health, Bacteria in Well Water (updated 2025-08-01) · checked October 5, 2026
- Minnesota Department of Health, Well Testing, Results, and Options (updated 2026-10-02) · checked October 5, 2026
- UC Cooperative Extension San Diego County, How to Measure Nitrate Concentration (G. Spinelli, February 2022) · checked October 5, 2026
- NC State Extension, Nitrate in Drinking Water (AG 473-4, reviewed 2023-11-29) · checked October 5, 2026
- Water Systems Council (wellcare), Arsenic & Well Water information sheet, pp.1-2 · checked October 5, 2026
- Penn State Extension, Iron and Manganese in Private Water Systems (2025-05-29) · checked October 5, 2026
- Penn State Extension, Water Softening (updated 2025-09-08), Table 1 · checked October 5, 2026
- Penn State Extension, Hydrogen Sulfide (Rotten Egg Odor) in Water Wells (updated 2024-12-10) · checked October 5, 2026
- Penn State Extension, Corrosive Water Problems (updated 2025-05-29) · checked October 5, 2026
- Nebraska Extension, Drinking Water: Iron and Manganese (G1714, revised May 2021), pp.3-6 · checked October 5, 2026
- Virginia Cooperative Extension, Household Water Treatment (442-670, 2024), pp.2-9 · checked October 5, 2026
- Wisconsin DHS, Treatment Devices for Private Well Contaminants (P-03494, 11/2024), pp.1-3 · checked October 5, 2026
- NSF, NSF Standards for Water Treatment Systems · checked October 5, 2026
- U.S. EPA WaterSense, Guide to Selecting Water Treatment Systems (832-F-24-024, November 2024), pp.4-8 · checked October 5, 2026
- Marlo Inc., Water Chemistry and Treatment (Form 1-246-R1), p.1 · checked October 5, 2026
Method: Limits are copied from EPA's primary, secondary, lead and PFAS pages. Public-health steps are quoted from CDC, EPA, the Minnesota Department of Health, NC State Extension and the Water Systems Council. Treatment options and the equipment order come from Penn State, Nebraska and Virginia Cooperative Extension, Wisconsin DHS and NSF, all checked 2026-10-05. The tool compares numbers; it does not diagnose a well, and we have not tested any water.