We installed this vitamin c shower filter(very easy, universal) and instantly felt the difference (less itch, softer water). We went through the first filter quickly, however, we have 5 people using the same shower because the kids like our large shower. With 5 people taking about 6 hot showers per day this filter lasted 2 weeks. One or two people this filter should last a month or longer depending upon the length and temperature of the water flow. I waited two days before I replaced this Vit C cartridge and we felt the chlorine-itchy skin almost immediately. Even though this unit came with 3 total cartridges I bought 3  more. I'm considering ordering more of these for the other showers in the house. It's ashame not to install these everywhere. If you are worried about cost, compare this to cost of 'under filtering' with a different medium and also the cost of Vit C serum for the skin.