Understanding Water Testing

Not all water testing reports are the same, but they have similar sections. Most reports have a Cover Page, Case Narrative Section, Results Section, Quality Control Section, and a Chain of Custody. More information on report sections and definitions for commonly used terms are provided below. If you have specific questions about your results, you may also contact the EPA Water Systems Council—Well Care Hotline at (888) 395-1033 or your local Health Department.

Cover Page

This section will include the name of the laboratory that performed the analysis of your sample, an ID number that identifies your sample, the date the analysis was completed, and may include additional routing information.

Case Narrative

This section contains a description of any issues or special notes for your report.

Results Section

This section may have various names in your report: Analysis Report, Client Sample Results, Preliminary Results, etc. It is the section that contains the results for your sample.

The left side of the page lists chemicals that were tested and may be labeled as Analysis Name, Parameter, Analyte, or something similar. Some laboratories include a CAS Registry Number, a unique identifier for each chemical.

The middle of the page contains the results from your water in the column labeled Result, As Received Result, or something similar. A number for each chemical labeled the Reporting Limit (RL), Limit of Quantitation, Method Detection Limit or Method Reporting Limit will also be provided. This number is the minimum level of the chemical that can be detected by the instrument used. The following symbols could be used to describe your result if it is below this number, and all have the same meaning:

N.D.: none detected

BMQL: below minimum quantitation level

< (followed by the RL): less than the RL

If none of the following are given, the chemical was detected in your sample and the amount is listed. Units are the increments used to measure the amount of a chemical in your sample. Most are listed in mg/L (milligrams per liter) or ppm (parts per million). Some of the results may be listed in μg/L (micrograms per liter) or ppb (parts per billion). To convert from mg/L to μg/L, divide by 1000.

Some reports may have every chemical that was detected in the sample in boldface. If a chemical has a special symbol or flag next to it, it may tell you that the chemical is discussed in the case narrative section. All reports should have a section to explain any symbols used.

The right side of the page may contain other notes from the laboratory such as the name of the analyst, the date the sample was analyzed, and/or the dilution factor. Notes may also tell what method was used to test for a chemical.

It may look like a test for a particular parameter was performed more than once. This may be due to testing with multiple methods or may be part of the lab’s quality control information.

Note that some results sections will include Surrogate Recoveries. These are not chemicals that were detected in your water; they are chemicals added and then removed by the laboratory to make sure their tests are working correctly. The chemicals used for this purpose may include Dibromofluoromethane; 1,2-Dichloroethane-d4; Toluene-d8; and 4-Bromofluorobenze, among others. 

Quality Control

This section may also be called QC Sample Results, Quality Control Data, Quality Assurance, or something similar. This section shows that proper methods were followed and can be used by the laboratory to check the accuracy of your results.

Chain of Custody (COC)

This is the form filled out by the collector of the sample for the laboratory and ensures that the sample was received in the proper condition.

The Ohio State University also has an excellent website for interpreting water testing results form commercial labs: