Operator terms · Water
What is backwash in water treatment?
Backwash is reversing the flow through a filter to clean it, pushing water back up through the media to lift out the trapped particles and flush them away. Filters are backwashed regularly so they keep removing turbidity. It is routine operator maintenance in a surface-water plant.
Last reviewed 2026-08-03
Why filters need it
As a filter removes particles, the trapped material clogs the media and the filter works harder. Backwashing lifts that material out so the filter runs clean again.
How it works
The normal downward flow is reversed, sending water up through the media to loosen and carry away the particles, which are sent to waste.
Common questions
- Why backwash a filter?
- To flush out the particles it has trapped so it keeps working.
- How often?
- Regularly, as the filter loads up; operators watch its performance.
- Where does the backwash water go?
- To waste, carrying the flushed particles away from the filter.