This is a replacement filter cartridge for the .35 micron post filter which is an additional accessory for the Rhino municipal whole house filter and and is included with the Rhino well water filter . It is designed to remove particles down to .35 microns which is 60 times smaller than the human eye can see. Some of the contaminants removed would include insoluble minerals as well as cysts. It is used as a water polishing agent and is an additional level of protection for you and your family in case of a cryptosporidium or giardia outbreak. It is recommended this post filter be replaced every 9 to 12 months. To find out more about how this filter can benefit you please call 1-866-523-4099 and talk to one of our expert water consultants.