What is the primary purpose of backwashing a sand filter?

The primary purpose of backwashing a sand filter is to remove trapped particles. Over time, as water flows through the sand, various contaminants like dirt, sediment, and organic material become trapped within the sand medium. This buildup can reduce the efficiency of the filter, decreasing its ability to clean the water effectively. During the backwashing process, water is reversed through the filter, which dislodges these trapped particles and flushes them out, restoring the filter's effectiveness and improving the flow rate of water through it.

Choosing other options would not accurately reflect the function of backwashing. While increasing the flow rate may be a consequence of effective backwashing, it is not the primary purpose. Adjusting the chemical balance pertains to the treatment of water rather than the mechanical filtering process. Lowering the water level does not relate to the function of backwashing, as the process itself focuses on cleaning the filter rather than manipulating the water level.