Know Your Numbers
Reading a New Jersey Well Water Test Result
A test result is a page of numbers with no explanation attached, and half of them aren't health limits at all. This page is a translation, not a diagnosis.
The first thing to understand: primary versus secondary
- •An MCL, a Maximum Contaminant Level, is the maximum level of a primary contaminant allowed in drinking water under the Safe Drinking Water Act.
- •An action level is a concentration of certain primary contaminants — lead and copper — at which treatment requirements may be triggered.
- •A recommended upper limit is the optimal range for a secondary contaminant, such as iron, manganese and pH, under New Jersey's Safe Drinking Water regulations.
The practical takeaway: exceeding a recommended upper limit is a staining, taste or colour problem. Exceeding a primary MCL is a different category of thing.
The numbers
| Parameter | New Jersey figure | What kind of limit |
|---|---|---|
| Arsenic | 5 micrograms per litre | Primary MCL |
| Nitrate | 10 mg/L | Primary MCL |
| Lead | 5 micrograms per litre | Action level |
| Gross alpha particle activity | 5 pCi/L initial, 15 pCi/L final | Primary MCL |
| Iron | 0.3 mg/L | Recommended upper limit (secondary) |
| Manganese | 0.05 mg/L | Recommended upper limit (secondary) |
| pH | 6.5 to 8.5 optimum range | Secondary |
| Total coliform / E. coli | Present or absent | Primary |
| Uranium | Required PWTA parameter in Sussex, Passaic & Warren Counties | Primary — see NJDEP reporting form |
Arsenic — 5 micrograms per litre, a primary MCL. NJDEP adopted this standard in January 2006; the federal standard is 10, so New Jersey's is the stricter of the two.
Nitrate — 10 mg/L, a primary MCL.
Lead — 5 micrograms per litre as reported on New Jersey's private well test reporting form; an action level at which treatment requirements may be triggered.
Gross alpha particle activity — 5 pCi/L initial, 15 pCi/L final, a primary MCL.
Iron — 0.3 mg/L, a recommended upper limit for a secondary contaminant. Aesthetic — staining, taste, colour. Not a health violation.
Manganese — 0.05 mg/L, a recommended upper limit for a secondary contaminant. Aesthetic — staining, taste, colour. Not a health violation.
pH — optimum range 6.5 to 8.5, a secondary contaminant.
Total coliform and E. coli — reported as present or absent, not as a concentration.
Uranium — a required parameter in Sussex, Passaic and Warren Counties. The standard is published by NJDEP; we do not publish a uranium figure here. Point readers to the NJDEP reporting form and to NJDEP for the value.
Gross alpha, properly explained
Gross alpha measures radioactivity in well water coming from radium, uranium and/or radon, all of which occur naturally in almost all rocks and soils. NJDEP's approved method is a 48-hour rapid gross alpha test, analysed within 48 hours of the sample being collected.
- •Below 5 pCi/L, NJDEP recommends no further action.
- •Between 5 and 15 pCi/L, NJDEP recommends testing for radium-226 and radium-228.
- •Above 15 pCi/L, NJDEP recommends further testing for uranium, radium-226, radium-228 and radon, and recommends installing treatment after the source of the radiation has been identified.
Gross alpha became a required parameter in 12 counties in 2008 and a statewide parameter in 2018, so NJDEP notes there may not be much data for a given area yet. The piece of advice that matters most and that costs us equipment sales: find out which radionuclide you actually have before you buy a system for it, because the treatment is not the same for all three. That is NJDEP's own sequence and it is the right one. See NJDEP's gross alpha page.
What each result usually leads to
- •Coliform leads to disinfection and finding the entry point. See well water chlorination.
- •Nitrate points at something on the surface and is worth investigating rather than only filtering.
- •Arsenic has specific treatment and is not addressed by a softener.
- •Iron and manganese are oxidation-and-filtration problems. See iron, manganese & sediment filtration.
- •Hardness is a softener question. See water softening & hard water.
- •Gross alpha needs identification first.
After treatment, test again
NJDEP's advice: always test the water again after a treatment system is installed, to confirm it is properly treating the water, and maintain the system to the manufacturer's instructions regardless of what kind it is. The practical version: a system nobody has tested behind is a system nobody knows is working.
Use a certified lab
New Jersey publishes a list of NJDEP certified drinking water laboratories, and NJDEP's instruction is to use one for any drinking water test. For the 48-hour rapid gross alpha test many certified labs are out of state and arrangements are made through a New Jersey lab for collection and shipment. See NJDEP's testing page.
Questions we get on this one
My result says 'present' for coliform, is my water unsafe?→
A present result for total coliform means the bacteria showed up in the sample and the well needs to be disinfected and the entry point found. If E. coli is present, that is a more specific indicator. The response is disinfection and finding how bacteria got in, not panic. Retest through a certified lab after the chlorine has cleared.
What's the difference between an MCL and a recommended upper limit?→
An MCL, a Maximum Contaminant Level, is the maximum level of a primary contaminant allowed in drinking water under the Safe Drinking Water Act. A recommended upper limit is the optimal range for a secondary contaminant — iron, manganese, pH — under New Jersey's Safe Drinking Water regulations. Exceeding a recommended upper limit is a staining, taste or colour problem. Exceeding a primary MCL is a different category of thing.
Why is New Jersey's arsenic standard different from the federal one?→
New Jersey adopted a standard of 5 micrograms per litre in January 2006; the federal standard is 10. New Jersey's is the stricter of the two. Both are set by NJDEP for the purposes of this page.
My gross alpha came back at a number between 5 and 15, what now?→
Between 5 and 15 pCi/L, NJDEP recommends testing for radium-226 and radium-228. Above 15 pCi/L, NJDEP recommends further testing for uranium, radium-226, radium-228 and radon, and treatment after the source has been identified. Below 5 pCi/L, NJDEP recommends no further action. Find out which radionuclide you actually have before you buy a system for it, because the treatment is not the same for all three.
Can I retest to get a better result?→
You can retest, and a retest is in fact NJDEP's advice after any treatment system is installed, to confirm it is treating the water. But retesting to get a different number on the same untreated well is not a strategy — water changes day to day, and a clean retest does not erase a failed one. The point is to find out what's there and deal with it.
Why wasn't uranium on my neighbour's test in another county?→
Uranium is a required parameter under the Private Well Testing Act in Sussex, Passaic and Warren Counties (and several others). It is not required in every county. Mercury, for example, is required in a different set of counties. The required parameters depend on where the well is.
Questions about your own well?
Call (862) 276-0328Last reviewed September 2026. Rules change, and these pages summarise what the agencies say rather than giving legal advice. Confirm anything that matters with the agency named on the page.