The most effective greywater “filter” is biologically-active soil covered in mulch! In simple systems, filters usually cause more problems than benefits. Filters need regular maintenance–not a fun job–and if the filter isn’t changed the system will fail. Filters remove large particles (hair, lint, etc), but not salt or dissolved chemicals. If you design your system in such a way that large particles won’t clog the system, then you don’t need a filter: Design so that larger particles in the greywater will be caught in mulch and compost, while the water soaks down to the dirt and irrigates the roots of plants. We recommend systems with no filters other than well-mulched soil.
High tech systems (into drip irrigation or for toilet flushing) do require filters. These systems need automatic cleaning of the filter to be long lasting.
We discuss several systems that filter greywater to be used for irrigation or toilet flushing on the Manufactured Systems page.