Which public water systems must comply with the Capacity Development Requirements according to Article 6?

The correct answer highlights that both Community and Non-transient Non-community Water Systems must comply with the Capacity Development Requirements starting after October 1, 1999. This is significant because these types of water systems are larger and typically serve a stable number of users, which means they have a greater responsibility to ensure they can maintain compliance with public health standards and provide safe drinking water.

The Capacity Development Requirements are designed to ensure that new and existing systems have the necessary technical, financial, and managerial capacities to be sustainable and effective in delivering safe drinking water. By applying these requirements to Community and Non-transient Non-community Water Systems, regulators can promote better infrastructure and operational practices.

Focusing on the other options, it’s crucial to recognize that not all water systems have the same obligations. Transient Water Systems do not serve the same population consistently and thus may not face the same rigorous requirements. Additionally, stating "All Water Systems Regardless of Date" would be too broad, as it would improperly include systems established before the specified date that may not necessarily be subject to the same compliance mandates. Therefore, the targeted approach established in the correct answer aligns with the regulatory framework designed to enhance public health protections through capacity development.