When is a filter backwash cycle for a sand filter considered complete?

A filter backwash cycle for a sand filter is considered complete when the backwash water appears clear in the sight glass. This indicates that the sand inside the filter has effectively removed impurities and debris, allowing for a clean flow of water through the filter. During the backwash process, dirty water is flushed from the filter, and it initially may contain suspended particles and contaminants. Once the water flowing through the sight glass is clear, it suggests that the filtering media has been properly cleaned and is functioning optimally, ready to resume filtration of clean water.

While other conditions may indicate the backwash is in process or influence operational choices, they do not specifically confirm that the filtering media has returned to an optimal state for filtration. For example, a two-minute run is arbitrary and does not guarantee clear water. Similarly, reaching a pressure of 50 psi could indicate an issue with the filter or system but is not a valid measure of backwash completion. With no water flow through the system, it might suggest a problem rather than a successful backwash. Therefore, observing clear backwash water is the most definitive indicator of completion.