RO/DI hooked up to cold AND hot supply

[hillegom]

If the pressures in house plumbing, hot and cold, are equal, why not put a john guest 1/4" ball valve in the hot water line and open it a smidgen. You would then use two one way check valves so that the hot and cold doesn't mix.

Just as an aside, hot water tanks have sacrificial zinc anodes in them.
they corrode before the steel does. Your RO membrane would have to take on the additional job of removing zinc. But I do not think that there would be very much of that in the water. The anodes last at least 5 years, the length of time most hot water tanks are warranted for.