Since it was hard to maintain purity with only ion exchange resin, we inserted RO membrane. It can be set easily if it is a special case. However, since the connection port is loose and water leakage occurs, it occupied considerably. Naturally, the purity is improved and the lifetime of the ion exchange resin seems to be extended. I think that raising the water pressure with the boost pump is the mast to earn the flow rate. The price was not the cheapest in the available RO.