The confusion of filters and water softened.
water softener remove calcium and magnesium leaving your water scale free.
filters can remove many things we normally use them on hard water to improve the flavour of the water by dealing with chlorine, particles and other nastys.
Here is a filter set that a customer had been using for 20 years. The tap had started to drip.
We replaced the unit with this tap with the filters hidden in the cupboard below. We even send our customers reminders when their filters need changing.