Water Resources 5 Stage Reverse Osmosis Filter Pack. For Water Resources, and International Filter, Envirotech 5 stage, and other 5 stage RO systems with 2 post filters. Includes all filters, o-rings, and adaptors for a Water Resources 5 stage RO system filter change. keep your RO system at peek performance with quality filters. Detailed instructions included. ROFCTK, Filter change tool kit available separately.