Backwashing

Backwashing is the process of reversing water flow in the sand filters, flushing trapped particles and material (debris) to waste (sanitary sewer).

When to Backwash

Per PHTA guidance, backwashing the sand filters is necessary when the gauge pressure increases 8 to 10 PSI above the starting pressure (typically about 9 to 10 PSI).

In other words, when the tank gauge shows 17 to 20 PSI, backwashing is necessary. That said, depending on other parameters (such as flow rate), backwashing before this threshold may be necessary. To maintain proper filtration, the system must have sufficient flow to fully turn over every 6 hours (4 times daily).

Excessive Backwashing

Excessive backwashing will result in an inability to remove smaller particles. Sand filters are most effective at trapping small particles when they are at the latter (higher pressure) part of the cycle. Therefore, premature backwashing may result in lower water clarity.

Backwashing also dumps a tremendous amount of water into the sanitary sewer, often leading to a necessary fill post-backwash. Reducing the frequency of backwashing (to only when it's deemed necessary versus on a too-frequent interval) conserves water and can improve overall water clarity.

Process

The process for backwashing is as follows: