Answer

The filter change timescale will depend on the type of filter, and how much the RO water purifier is used. Also, the clarity / purity of the water feed to the RO unit.

You are most likely to need to change the 3 pre-filters (after approx. 12 months or 15,000 litres of pure water has been generated) or the resin deioniser cartridge (the colour of the resin changes when you need to replace it - no timescale guide is given for this by the manufacturer). The Reverse Osmosis (RO) membrane should last at least 2 years, although again this will depend on how much the apparatus has been used. 

There is a setting on the digital controller of the main unit which will tell you when any of the filters need changing, so you know which one(s) to change.

The filter cartridges are easy to change – simply unscrew any which need changing and replace with a new filter cartridge.

The relevant codes for the filters are:

WAT-500-200 : DEIONISING RESIN CARTRIDGE

WAT-500-250:  3 PRE-FILTER PACK

WAT-500-300:  RO MEMBRANE