I would recommend against running a
RO/
DI into a reservoir "all the time", even if you have an automatic shut-off or other overflow protection. The reason is that when you have a regular full flow over your
RO membrane, everything is fine. When you start to slow down that flow, either by way of filling a pressure holding tank or by a float valve, when the water stops the dissolved solids (that can get through) will have more time and opportunity to get past the membrane, and you will end up with high
TDS water on the 'clean' side. If you don't flush this out before running it through your
DI, you'll burn out your
DI a lot faster. So my recommendation on
RO/
DI is only use it when you need it, run it full-flow ONLY, and ALWAYS run about 1 gallon out of the the
RO 'clean' side before running it through your
DI.
In my home system, which has 2 pressure tanks and a 25 GPD membrane, my
TDS out of the sink tap is over 300 because we only use about 1/2 gallon in one shot, and with 2 4 gallon tanks, the 'clean' side flow is just a trickle compared it if they're both empty, so the low flow allows more time for DS to get by.
I verified that this is the case by having a long discussion with someone who has been in the
RO industry for over 20 years.
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