Microline Sediment Pre-Filter S7011. For all Microline systems. This filter removes any particles that may be in your water before it reaches the sensitive membrane. This cartridge should be changed every 6 - 8 months. If you have no other water filtration or treatment equipment before your RO system, you should change this filter every 3 - 4 months. Remember there are no shipping charges for over $50.00 and these won't go "stale" so stock up on supplies.