What is the typical duration a Non-Transient Non-Community system must serve its population?

In the context of Non-Transient Non-Community (NTNC) water systems, which serve a specific population on a regular basis but do not qualify as a community system, the typical requirement is to provide water service for at least six months each year. This classification applies to facilities such as schools or workplaces where the same individuals are present for an extended period.

The need to serve this population for six months emphasizes that the system must maintain water quality and supply for those who rely on it consistently during significant parts of the year, rather than sporadically. This duration ensures that NTNC systems are equipped to provide a dependable water source for the population they serve, which is crucial for both health and safety.

The other options suggest either shorter service periods or an all-year-round requirement, which are not aligned with the classification and operational guidelines established for NTNC systems. Therefore, recognizing that an NTNC system is structured to reliably serve a defined group for a substantial part of the year is key to understanding why this six-month service duration is the correct and appropriate answer.