Mixed resin filters in most cases serve as the last line of filtration. They are generally installed after reverse osmosis stages. This method reduces the electrical conductivity of water below 0.1 μSiemens, which is usually a requirement of the pharmaceutical or energy industries.

The filling of this filter does not have the possibility of regeneration as is the case with sand filters or softeners, so it must be replaced with a new one after a certain production time. Today, these filters are used less and less for the reason that the same result can be achieved by electrodeionization, a method that requires less maintenance and is more practical to use in most systems.