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Well water test reports use specific terminology that isn’t always explained. This glossary covers the terms you’re most likely to encounter.
- MCL is the EPA’s regulatory benchmark, commonly referenced even for private wells.
- Total coliform indicates potential contamination pathways; E. coli indicates fecal contamination specifically.
- Nitrate has a specific infant health concern at elevated levels.
- Hardness is a mineral/nuisance issue, generally not a direct health concern.
Regulatory and Measurement Terms
MCL (Maximum Contaminant Level): the EPA’s legal limit for a given contaminant in public water systems, commonly used as a reference benchmark for private well results even though it isn’t legally binding for private wells [1].
mg/L (milligrams per liter): the standard unit for most chemical contaminant measurements, roughly equivalent to parts per million (ppm).
Bacterial Testing Terms
Total coliform: a broad category of bacteria used as an indicator of potential contamination pathways, not necessarily harmful itself but a warning sign. E. coli: a specific coliform subgroup indicating fecal contamination and a more direct health concern if present.
Common Contaminant Terms
Nitrate: a compound from fertilizer, septic systems, or animal waste, with a specific health concern for infants (blue baby syndrome) at elevated levels [2]. Hardness: mineral content (calcium, magnesium) affecting scale buildup and soap efficiency, not typically a health concern but a common nuisance issue.
Terms About the Limits of the Test Itself
Detection limit: the lowest concentration the analytical method can distinguish from zero. Reporting limit: the lowest concentration the lab will state as a number, usually somewhat above the detection limit, because values below it are less reliable. Non-detect, often printed as ND: the analyte was not found above the reporting limit, which is not identical to a true zero.
That last distinction causes more confusion than any other item on a report. ND means the method did not see it at the level the method can see. If a very low concentration matters for your situation, the question to ask the lab is what reporting limit they used and whether a more sensitive method is available.
Treatment and Equipment Terms
Point of entry, abbreviated POE: treatment installed where water enters the house, so it treats everything. Point of use, abbreviated POU: treatment at a single fixture, most often an under-sink unit serving one tap. Micron rating: the particle size a filter is designed to capture, where a smaller number is a finer filter and typically a greater restriction on flow.
Media: the material inside a treatment vessel that does the work, which is replaced or regenerated on its own schedule. Backwash: reversing flow through a vessel to flush trapped material out to a drain. Regeneration: the cycle a water softener runs to restore its resin, which is why a softener needs both a drain connection and a salt supply.
Sampling Terms You Will See on the Instructions
First draw: a sample taken from a tap that has been sitting unused for a stated period, which captures what the standing water picked up from the plumbing. Flushed sample: taken after running the tap for a specified time, which is closer to what the well and any treatment are delivering. The two answer different questions and are not interchangeable.
Chain of custody: the documented record of who handled the sample and when, from collection to analysis. Holding time: the maximum interval between collection and analysis for a given test, beyond which the result is no longer considered valid. Both terms show up most often in real estate transactions, where documentation is part of what is being purchased.
FAQ
What’s the difference between total coliform and E. coli on my test report?
Total coliform is a broader indicator bacteria category; E. coli is a specific subgroup indicating fecal contamination and a more direct health concern.
Does non-detect mean there is none of that contaminant in my water?
It means none was found above the reporting limit the lab used, which is a different statement. For most household purposes those amount to the same practical answer, but if a very low level is specifically relevant to your situation, ask the lab what reporting limit applied and whether a lower one is available.
What is the difference between mg/L and ppm on my report?
For water they are used interchangeably in practice, since a liter of water weighs close enough to a kilogram for the conversion to be one to one. If you see both units on the same report, they are not describing different things.
Why does my report list a limit next to some results but not others?
Regulatory limits exist for the contaminants that are regulated in public water systems, and many parameters a lab measures simply do not have one. A result with no limit beside it is usually informational, such as hardness or pH, rather than an omission on the lab’s part.
This glossary is for general orientation — refer to your specific lab report for terms not covered here.
References
- National Primary Drinking Water Regulations. U.S. Environmental Protection Agency
- Potential Well Water Contaminants and Their Impacts. U.S. Environmental Protection Agency
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Content is for informational purposes only and is not medical advice; consult a qualified healthcare provider before starting any supplement. As an Amazon Associate we earn from qualifying purchases.
