Which of the following is NOT a purpose of filter underdrains or bottoms?

The selected answer emphasizes that removing chemicals from water is not a purpose of filter underdrains or bottoms. Filter underdrains primarily serve specific functions related to the filtration process.

Their key role is to support the filter media, ensuring that it remains in place while allowing water to flow through. This structural function is critical to maintain the integrity of the filtration system. Additionally, underdrains facilitate the effective removal of backwash water, which cleans the filter media, thereby extending its life and maintaining system performance.

Another important function of underdrains is to enhance filtration efficiency. By providing an optimal flow path for water, they help maintain consistent hydraulic conditions during the filtration process, contributing to the overall effectiveness in reducing suspended solids and improving water quality.

In contrast, while chemical removal is an important goal of the overall filtration system, it is not directly associated with the role of the underdrains or bottoms. Their design does not involve chemical treatment; instead, that function is primarily fulfilled by the filter media itself or other treatment methods in the water treatment process. Thus, this distinction clearly identifies why the correct answer pertains to the purpose of filter underdrains.