A swimming pool filter should be backwashed when the pressure gauge shows a pressure rise of 8 to 10 pounds above the pressure when the filter is clean. Backwashing cleans the filter by reversing the water's flow through the filter.
Backwashing the filter uses extra water. Pool owners should limit the number of times the filter is cleaned, as well as the amount of time doing it. Two or three minutes, or until the water in the sight glass runs clean, is best. Following this procedure too often decreases the filter's effectiveness. Using water from this process to water trees or shrubs is recommended, as it is often illegal to dump it into storm drains or allow it to flow onto the street.