What is the acceptable percentage of total coliform samples for a water system that collects at least 40 samples per month to remain in compliance?

For a water system that collects at least 40 samples per month, compliance with the total coliform rule is determined based on the acceptable percentage of samples that can test positive for coliform bacteria. The correct percentage is no more than 5%.

This threshold is set to ensure the safety of drinking water and public health. Total coliform bacteria are indicators of possible contamination and can signify the presence of harmful pathogens. By allowing a maximum of 5% positivity in a large number of samples, regulators balance the need to be alert to contamination while acknowledging that some level of bacteria can occur without indicating a system failure.

Thus, maintaining a positivity rate above 5% would indicate a significant risk and non-compliance, potentially leading to health advisories or remedial actions, while staying within this limit signifies that the water system is considered to have an acceptable level of water quality.