A solenoid valve allows you to fill your tank directly from your plumbing system which eliminates the need for an ATO reservoir. Normally closed valves are used for autotopoff, they open when powered, and are closed when not powered. An ATO controller is normally used to power a solenoid valve, but you could also power it with a programmable timer along with more frequent monitoring

If you install the solenoid valve on your RO's output you will need an auto shutoff valve and check valve on your RO system to prevent it from generating wastewater when the solenoid is closed.

Direction matters! There is an indicator on all valves that shows the water flow direction.

Using a solenoid valve means connecting your tank to an endless supply of water, therefore some type of fail-safe protection is recommended. Use a double switch controller instead of a single or two single switch controllers in series instead of a double, two solenoid valves in series, a mechanical float valve as a backup to the solenoid valve, a timer to limit the ATO so it only runs for a few minutes a few times per day, a water alarm to alert you if a water is detected on your floor, a flowlok to shutoff the water if water is detected on your floor, etc.