[mike31154]

When setting this up try to ensure the RO/DI system runs for a reasonable length of time to fill a reservoir for top off. Many folks use a single float valve feeding directly into the sump and the system switches every few minutes which is not a good way to run your RO/DI. It generally takes several minutes for the RO/DI TDS to drop to optimum level after the system is pressurized, so if your unit switches every few minutes, you'll have major TDS issues with your top off water. Furthermore, the excess TDS going to the DI in that first minute or so, will ensure your DI media is used up in short order.

Automation can be a wonderful thing and I have the auto shutoff valve on my system, but I still make RO/DI water by manually switching the source on and making at least 5 gallons at a time. I bypass the DI stage for the first minute and send that production water to my RO jug for drinking water. I've never been able to get my auto shutoff valve to work consistently or reliably and do not trust the things. I collect my waste water in large containers to use around the house & garden and do not wish to take the chance of a flood in the event of an auto shutoff valve malfunction. As for electrical solenoids, also wonderful devices, but more electrics involved (increased complexity) and simply another possible point of failure.