Drinking water standards generally specify that a water is safe if testing reveals no more than

The guideline regarding drinking water standards is focused on ensuring safety and minimizing health risks associated with microbial contamination. The correct answer of having 1 positive sample out of 40 indicates that the water system is operating within acceptable limits for presence of coliform bacteria, specifically when considering fecal coliforms, which can indicate the presence of pathogens that affect human health.

This standard is often related to the Total Coliform Rule set by the Environmental Protection Agency (EPA), which is designed to identify contamination events. Essentially, if only one sample in a set is positive, it suggests that the water supply is generally safe and that significant contamination is unlikely. Regular monitoring with this sampling frequency provides public health protection while recognizing that occasional presence of coliform bacteria does not automatically signify imminent danger.

Considering the other options, they may suggest higher allowable limits or different testing parameters that don't align with the established standards for safe drinking water. For example, 10 positive samples or 50 coliform organisms would indicate a higher level of contamination than what is acceptable, while 50 organisms per 200 ml represents a different quantification that doesn’t fit the safety threshold set by regulatory agencies. Hence, option C accurately reflects the established threshold for ensuring that water remains safe for consumption.