Why is surface wash used during backwashing?

Surface wash is employed during backwashing primarily to prevent mudballs from forming in sand and other filter mediums. As filters operate, particulate matter can accumulate and compact, leading to the formation of mudballs—clumps that can obstruct flow and reduce the filter's efficiency. The application of surface wash dislodges these clusters, ensuring the filter medium remains clear and functional. This process enhances the overall filtration performance by maintaining an optimal flow rate and preventing dead zones where water may stagnate.

In the context of backwashing, the focus is on restoring the filter to a state where it can effectively capture contaminants without being hindered by build-up. While other reasons such as preventing algae growth, clogging of filters, or enhancing chemical dosing may be related to filter maintenance and operation, they are not the primary purposes of surface wash during backwashing.