The use of pre-filters is important in prolonging the life of the (expensive) high pressure pump in your watermaker. Regular replacement of pre-filters is recommended. See your manual for specifics.
• Sediment pre-filters are pleated and rated in microns, according to the size of the particles filtered - the smaller the number, the finer the filter. Typically, 5 microns is “standard”, but for water with a high concentration of particulates, a 20 micron filter or 75 micron plankton filter may be installed before the 5 micron filter to prevent it from clogging prematurely