What is an important purpose of filter underdrains?

The primary purpose of filter underdrains is to efficiently manage the flow of water through the filtration system. Specifically, the correct choice highlights the role of underdrains in delivering backwash water under the filter media. During the backwashing process, backwash water is directed through the underdrains to help dislodge and remove accumulated particles, allowing for a thorough cleaning of the filter media. This process is essential for maintaining the efficacy of the filtration system, as it prevents clogging and ensures that the filter continues to operate effectively.

In contrast, the other options represent functions that are either secondary or not the main purpose of underdrains. For example, while transferring filtered water to storage is essential in a water treatment plant, it does not specifically relate to the function of underdrains, as underdrains are primarily involved in the backwash process. Similarly, filtering out particles in the water pertains to the filter media itself rather than the underdrains. Finally, the removal of mudballs is a specific issue but does not capture the fundamental purpose of underdrains in the context of water treatment operations.