It's not at all unusual for the unti to run for a few after the filtered water is shut off, especially if you have a DI
canister.... it's just building up some pressure before activating the cut-off. As long as all the fittngs are connected properly, and it's not leaking you're fine.
Now, personally, I don't like using an RODI
system like that.... it's very inefficient. RO
membranes work at their optimum when they are allowed to run for a little while. Hooking a top-off directly to the RODI
system has it constantly starting and stopping, which anyone with an inline TDS
meter will be able to tell you, when the unit first comes on, the TDS
tends to be rather high and then slowly works it's way down as the unit runs for a couple of minutes.
Personally, I'd keep a jug or bucket of water and either run something like a BRS top-off pump or gravity feed your water to the top-off.