Water goes through a reverse osmosis membrane very slowly and people do not have the patience to wait a long time to get a cup of water. For this reason the residential RO units need a water storage tank to store the purified water. The RO tanks can delivery stable and constant water flow when the faucet is opened. The concern that pollutants might come from air or animals with the use an opened tank favors the use of a closed expansion tank.

Combining the advantages of metal and plastic barrels, this series mainly uses iron barrels as the base and a new-style plastic barrel covered with a plastic shell.