From the producer Replace PUR filters every six months. The life of the filter can vary depending on usage and condition of the local waters. Do not use with water that is microbiologically unsafe or of unknown quality without adequate disinfection before or after the system. Systems certified for cyst reduction may be filtered and disinfected water containing the cysts are used. People who need water of certain microbiological purity should consult their physician. Check the size of the first filter 4396510, 4396548, 9010, 4396508, 4396547 Read customer review 