What steps should be taken if a water sample tests positive for total coliform bacteria?

• A. Re-sample to confirm only
• B. Disinfect the distribution system and then re-test only
• C. Identify and remediate contamination source, but do not re-test
• D. Re-sample to confirm, disinfect the distribution system, identify and remediate contamination source, and re-test

Answer: (D)

When total coliform bacteria are found in a water sample, it signals possible contamination of the distribution system and prompts a full corrective response. The best approach is to follow a four-part action: re-sample to confirm the initial result, disinfect the distribution system and flush to remove contamination, identify and remediate the source of contamination to prevent recurrence, and then re-test to verify that the system is back to safe levels. Each step plays a crucial role: re-testing confirms whether the issue is real or a transient/false positive; disinfection reduces immediate bacterial levels and protects users; finding and fixing the contamination source stops future intrusion; and re-testing verifies that the corrective measures worked and the water meets safety standards. Doing only one or two of these steps risks leaving the system unsafe or unchecked.