back flush carbon water filter systems?

Answer 1

Carbon filters work by absorption.
Once the filter is full, it's dead and should be replaced.

Answer 2

Activated Charcoal Water Filters - These filters are used in many homes. Activated charcoal filters work by using charcoal as a filter medium. Activated charcoal is used in whole house filters, counter-top filters, and in many other water filters. The water supply is fed through the filter which screens out and traps many undesirable chemicals, particulates, and other impurities. An activated charcoal water filter is an example of a chemical process filter.

Activated charcoal is made by partially burning or distilling an organic material, and then it is specially heated or changed using a chemical process. Activated charcoal is almost pure carbon. Charcoal infused with oxygen has millions upon millions of little pores in its surface. The charcoal becomes very porous, and many undesirable elements adhere to the carbon as the water passes through the filter.

Due to the large surface area of the charcoal, and its ability to absorb a lot of unwanted minerals, elements, and gasses; this type of filter is in high demand. The surface area of just one gram of activated charcoal can range from 300 to 2,000 square meters. This allows a lot of space for impurities to stick to the charcoal in a filter. The drawbacks to activated charcoal filters are that once all the pores are full, you have to get a new filter; and it will completely ignore certain compounds and elements. You may need to have your water tested at a lab to determine what type of filter will best suit your needs.