The primary function of pre-stabilization filters is to protect the final membrane filters from colloidal particulate.
Most waters, while appearing visually clear, actually have a very large amount of suspended solids moving in solution. These are called colloids and are generally sub-micron in size. The main constituents of these colloidal species are ions (Fe3+) which have leached into the water from the source associated with organic material. These small, suspended particles are the major cause of membrane filter blockage, so their removal prior to membrane filtration will result in longer service life of the membranes and lower long-term running costs.