If a potable water test shows no FAC or TBR, what is the most likely interpretation?

• A. Water is safe
• B. No disinfection is required
• C. Possible Contamination
• D. Water quality is excellent

Answer: (C)

The important idea here is that a potable water test uses a residual disinfectant measure (FAC) and a microbial indicator (TBR) to gauge safety. If there is no free available chlorine left, disinfection isn’t being maintained. If you also don’t detect any bacteria, that might seem reassuring, but with zero FAC the result is suspicious: disinfection should suppress bacteria, and a test that shows no chlorine yet no bacteria could indicate the sample or the test itself was compromised. In practice, this pattern points to a possible contamination issue or a testing problem, so the prudent interpretation is that contamination could be present and the sample should be retested or the system evaluated before deeming the water safe.