A pure-water system should be chosen from the feed water and the work month, not from the number of filter stages printed on a product page. A DI-only path can be compact and simple, but its operating cost changes sharply with source-water TDS and water use. RO/DI adds equipment and setup, yet may reduce the load placed on resin when the route demands more water.
Use this section to keep the full chain visible: prefiltration, membrane or DI capacity, output rate, water-quality monitoring, hose and pole demand, refill access, transport and planned maintenance. Published capacity tables are useful starting points, not guarantees of field life.
Begin with the guide or calculator that answers the largest unknown. Then verify the exact manufacturer limits and replacement schedule for the configuration you are considering.