Quick Answer
Shower filter cartridge life typically ranges from 1 to 6 months depending on media: vitamin C is shortest (1-3 months), KDF/carbon longer (3-6 months). Hard water, more users, and longer showers shorten life. The housing itself lasts years; only the cartridge is replaced.
Problem
Shoppers conflate filter life (the housing) with cartridge life (the media) and underestimate how often cartridges need replacing.
Product Recommendation
ZOOSHEN cartridges are available in 1/2/4-Packs and via Subscribe & Save. The 4-Pack offers the best per-cartridge value.