What type of distribution system provides a circulating feed of water mains?

The correct answer is the loop distribution system. A loop distribution system is designed to create a network of interconnected water mains that circulate water throughout an area. This setup ensures that there are multiple pathways for water to flow, which enhances reliability and pressure management. In the event that one section of the main experiences a failure or maintenance issue, water can still be supplied from alternative routes, thereby maintaining service continuity.

Additionally, a loop system helps in balancing the flow of water, improves water quality by reducing stagnation, and facilitates easier maintenance as water flow can be redirected. This configuration is particularly beneficial for fire protection, as it allows for simultaneous use at multiple points without significantly dropping pressure.

The other types of systems have their own characteristics: a radial system has a central point with water flowing outwards, which can create pressure issues; a grid system, while it offers some redundancy, is not typically focused on circulation like a loop; and a branch system, which is more linear, can lead to areas with low pressure if a main breaks or is shut off.