Which method is the most reliable to determine the safety of a drinking water supply?

The most reliable method for determining the safety of a drinking water supply is a sanitary survey of the supply, which includes an assessment of the source, equipment, and distribution system. This comprehensive evaluation allows for an in-depth understanding of potential contaminants and the overall condition of the water system.

Conducting a sanitary survey helps identify sources of pollution, assesses risks associated with nearby land use, and evaluates the adequacy of treatment and distribution systems. By examining the entire water supply operation, public health officials can pinpoint vulnerabilities that may not be visible through sampling alone. This proactive approach is critical for ensuring that preventative measures are in place to protect public health.

In contrast, relying solely on the absence of coliform bacteria from three consecutive samples may not provide a full picture of water quality, as pathogens can fluctuate and may not be detected at all times. Similarly, the absence of chlorides or nitrates does not necessarily indicate water safety, since these compounds may not be present in all contaminated waters. Lastly, while a remote and isolated watershed area can contribute to water quality, it does not guarantee that contaminants are absent or that the system is properly managed. Thus, a comprehensive sanitary survey remains the most effective method for assessing the safety of drinking water supplies.