When should I replace this filter cartridges?

The actual lifetime of the filter cartridge depends on the quality of the local water and the water pressure. For optimal performance of the water purifier, replace the filter cartridge if one of the following situations occurs:
1. The filter cartridge has been used for one year.
2. The amount of water after purification is greatly reduced
3. The filtered water still has a bad smell, or remains turbid after purification.