I think basically your water supply to the RO/DI unit is controlled by a solenoid, the valve is actuated from a closed position to open; thus you would want a normally closed solenoid, for the purpose of fail safe operation, if you lose electricity for some reason, the switch closes thus shut off the water supply without any electricity. The idea of thankless is designed on this principal, however it is done. The unit I posted, will work like this; The floater will get to a point that will send a small voltage signal to the solid state controller, which will switch power on to the outlet box. From this point, the solenoid which is plugged into this outlet will get power, which will make the valve actuate and open, thus allowing for water to run through the RO/DI unit, the outlet of the unit can go directly to the sump (AKA tankless) or it can go to a tub, where in the tub other stuff can be dosed before being delivered to the sump, in the tub/bucket/tank etc.. will be a small ph with tubing that will feed your sump from the bucket, this ph will also need to turn on with one of these solid state units but here is the difference, the first unit is now located in the tub/bucket etc & the second is located in the sump. This way the tank/dousing tub etc. doesn't have to rely on the solenoid or RO/DI unit to make the water before feeding the sump. did I confuse me? LOL there is more than one way to skin this cat but now you hopefully get an idea. One thing in doing the storage unit, is it must be big enough that at no time will it ever need more water than the RO/DI unit can make. You can make several variants of this system, maybe MoJo will chime in on his automated design, I've read about it but maybe he can input a little more info, or maybe better ideas.
