What does washing-machine water filter mean in practice?
Depending on the cartridge, it captures sediment, doses polyphosphate or partly binds iron; not every version is intended for drinking water.
When does it matter?
A compact housing does not automatically soften all water, and an anti-scale claim does not mean hardness removal.
Which solutions are related to it?
Match the filter to the actual problem and water temperature, monitor flow and replace the cartridge as instructed.