It is recommended to replace the cartridge every three months to ensure maximum filter efficacy. This is because: The replacement cartridge is made of carbon, an organic material that can become a breeding ground for micro-organisms that, with time, can cause bacteria to proliferate. These bacteria build up behind the filter and contaminate the water. What's more, depending on how hard your local water is, the gradual build-up of limescale in the filter can restrict water flow. Recommended water temperature is between 5 and 38 °C.