Clients will occasionally request sampling and laboratory testing of their drinking water. Frequently, the ensuing discussion uncovers some common misconceptions about water contaminant testing in laboratories.
A typical request is please “lab test what’s in the water”. The assumption is drinking water samples are sent to the lab and the lab sends back a list of contaminants present (if any) along with the concentrations of each.
Laboratory Testing
Unfortunately, water testing in the lab does not proceed upon the open ended “what’s in the water” methodology. The fundamental reason becomes apparent upon realizing the “universe” of potential water contaminants includes over 18 million different compounds. Thousands more contaminants are developed by industry every year. Testing for each of these potential water contaminants would be exorbitantly expensive and literally take years.
Few people have trouble sharpening their focus. Usually the requester has some idea what contaminants are of concern and why. Frequent and legitimate concerns are contaminants like lead, arsenic, and copper. With the “universe” of contaminants cut down to size, the lab can get to work.
What’s ND?
Often the goal of testing is to prove there is no contaminant “x” in the water. Laboratory test results are often less than satisfactory in this regard. This brings up another common misconception about lab testing—the inability to prove something does not exist.
Test results often indicate the detected level of a contaminant as “ND”. ND stands for Not Detected. A careful reading of the test result notes will indicate “at a specified concentration”. Does a result of ND confirm the contaminant is not present in the water? No. The contaminant could be present at a lower concentration than the test equipment can resolve.
So often the end result is not a conclusive finding ruling out the existence of contaminant “x”, but a more vague statement about none detected over a certain threshold concentration.
Keep these concepts in mind when considering having water samples tested and you will not be disappointed.
