A potable water supply:

A potable water supply is defined as water that is safe for human consumption. This means that it must meet several quality criteria to ensure safety and health for people who drink it.

First, it is essential for potable water to be free of pathogenic organisms. This eliminates risks associated with waterborne diseases, which can be caused by bacteria, viruses, and parasites. Ensuring that the water supply is free of these pathogens is a fundamental requirement for it to be considered safe.

Additionally, potable water must contain safe levels of chemicals. This includes various minerals and other substances that can be present in water. Regulatory agencies set guidelines for these chemicals to prevent negative health impacts, ensuring that the water does not contain harmful concentrations of any chemicals.

Another important aspect of potable water is maintaining an adequate chlorine residual. Chlorine is commonly used as a disinfectant in water treatment processes. An appropriate level of chlorine residual helps ensure that any remaining pathogens are effectively killed, safeguarding the water supply as it travels through distribution systems to consumers.

Given that all of these factors—absence of pathogens, safe chemical levels, and sufficient chlorine residual—contribute to the definition of potable water, the correct choice is that a potable water supply must encompass all of these elements.