The unit has 3 filters and 1 membrane that must be replaced to produce the Blueprint Water to its highest quality. It is different for everybody as to when the filters need to be replaced. A general rule is 6-12 months if water is being filtered directly from a well. 12-18 months if water is being filtered from a city facility.
A general rule for replacing the membrane is that it lasts twice as long as the filters. Every other time you replace the filters, replace the membrane.