Read your water test results
Type or paste the numbers from a lab report, test kit or well test. For each line you see the federal or EPA reference it is compared with, what kind of reference that is, and what to do next.
Type or paste · each line from your report, test kit or well test
See the reference · legal limit, health goal or taste standard, named plainly
Know the next step · retest, certified treatment, your utility or our guides
- Pick what was tested and type the result
The reading appears here as you type.
Paste from your report
Read in your browser only. Nothing you type or paste is saved, sent to PurityMap or put in a link.
This is a reading of the numbers you typed, not medical advice.
We compare each number with the federal or EPA reference named beside it. We can’t check your lab, how the sample was taken, or anything not on your report. One sample is a snapshot: levels can change. For a health decision, talk to your doctor or local health department and confirm with a state-certified lab.
Read our health disclaimer and how we analyze water.
- One sample is not a water system’s compliance record. Federal limits are judged on a system’s results over time.
- Test strips and home kits are screening tools, not lab-grade results.
- We only read the substances in the table below.
- Private wells have no federal limits. EPA’s limits for public water are the usual reference.
- A result below a reference is not a health verdict. For substances whose health goal is zero, any amount is worth knowing about.
How to read a water test report
Most reports list, for each substance: the result, its unit, a qualifier such as “<” or “ND”, the lab’s reporting limit (RL or MRL), and often the federal limit (MCL) and health goal (MCLG). Read the result and its unit first, then compare it with the limit in the same unit.
Units, and how they convert
- ppm (parts per million)same as mg/L
- 1 ppm = 1 mg/L = 1,000 µg/L
- ppb (parts per billion)same as µg/L (also ug/L, mcg/L)
- 1 ppb = 1 µg/L = 0.001 mg/L
- ppt (parts per trillion)same as ng/L
- 1 ppt = 1 ng/L = 0.001 µg/L
- gpg (grains per gallon)hardness only
- 1 gpg = 17.1 mg/L as calcium carbonate
- pCi/L (picocuries per liter)radium, gross alpha
- radioactivity; no conversion to mg/L
Nitrate “as N” or “as NO₃”. EPA’s 10 mg/L nitrate limit is “as N” (the nitrogen in it). A result given “as NO₃” is 4.427 times larger for the same water: divide it by 4.427 before comparing. For nitrite “as NO₂”, divide by 3.285.
Kinds of reference
- MCL (maximum contaminant level)
- The federal legal limit for public water systems, judged on a system’s results over time.
- MCLG (maximum contaminant level goal)
- EPA’s health goal: the level below which no health risk is known or expected. It is not enforceable.
- Action level
- For lead and copper: if more than 10% of a system’s tap samples are above it, the system must take more steps.
- MRDL (maximum residual disinfectant level)
- The federal limit for a disinfectant such as chlorine or chloramine.
- Health advisory or guidance
- An EPA health-based level that is not a legal limit, such as the manganese lifetime health advisory.
- Secondary standard
- An EPA guideline for taste, smell, color or staining. It is not a legal limit and not about health.
- RL, MRL, MDL or “<”
- The lab’s reporting or detection limit: the lowest amount the test can measure.
“<”, ND, BDLmean not found, not zero
“<0.5”, ND (not detected) and BDL (below detection limit) all mean the lab did not find the substance above the lowest amount its test can measure. If that reporting limit is higher than the federal limit, the result can’t show whether your water is below the limit: ask a certified lab for a method that measures lower.
Every reference the reader uses
The same table the reader uses. Federal limits apply to public water systems; private wells have none.
41 references
Who the limits apply to
Federal limits apply to your utility’s system, judged on its results over time. Lead and copper use a system’s 90th-percentile result. A home result above a limit is worth retesting and reporting to your utility.
Find your water systemThe quality and safety of drinking water from private domestic wells are not regulated by the Federal Government under the Safe Drinking Water Act nor by most state governments and laws. Test your private well annually for total coliform bacteria, nitrates, total dissolved solids, and pH levels.
- →After flooding or land disturbance near the well
- →After the well is repaired or a part is replaced
- →When the water’s taste, color or smell changes
- →If someone in the home is pregnant or nursing
- →When an infant or child joins the household
Frequently asked
What does ND mean on a water test?
ND means not detected: the lab did not find the substance above its reporting limit, which may be shown as RL, MRL or a “<” followed by a number. It does not mean zero. If the reporting limit is higher than the federal limit, the result can’t show whether the water is below that limit.
Is ppm the same as mg/L?
In drinking water, yes. 1 ppm (part per million) equals 1 mg/L, 1 ppb equals 1 µg/L, and 1 ppt equals 1 ng/L. 1 mg/L is 1,000 µg/L, so 0.010 mg/L of arsenic is the same as 10 µg/L.
What does “nitrate as N” mean?
Labs report nitrate either as the nitrogen in it (“as N”) or as the whole nitrate ion (“as NO3”). EPA’s 10 mg/L limit is as N. To convert, divide a value given as NO3 by 4.427: 44 mg/L as NO3 is about 10 mg/L as N.
My result is above the MCL. What now?
Retest with a state-certified lab to confirm it. On city water, tell your utility: federal limits apply to the system’s results, and the utility can help check your service line and plumbing. Until you know more, you can use water from a filter certified for that contaminant, or bottled water, for drinking and cooking. On a private well, ask your local health department.