Most systems need a cold-water feed connection, filtered-water faucet and drain connection. Tankless systems add electricity and may use a smart faucet, while tank systems also need room for a storage tank.
Cold-water feed
RO connects to the cold-water supply with an adapter or feed valve. Confirm the valve size and shutoff condition before starting.
Drain connection
Reject water must go to the sink drain on most under-sink systems. Install the drain saddle in the position specified by the manufacturer to reduce noise and backflow problems.
Faucet installation
A dedicated RO faucet may require an existing accessory hole or drilling. Some direct-connect products avoid a dedicated faucet, while smart tankless systems may include proprietary faucets.
Flush and inspect
New carbon filters and membranes often require flushing. Check every connection under full pressure before leaving the cabinet closed.