You could do one of two things..
The simplest, and cheapest, is to get a larger capacity ro membrane and flow restrictor. You simply exchange the membrane that is in the housing, and replace the flow restrictor on the waste line. The largest capacity that I have sewn that fits in a standard sized housing is a 100gpd membrane. It will run about 35.00, and the restrictor about 10.00..
Or, you can go the big boy route, and do a piggyback or as brs(and filter guys) calls them saver units.. It's basically a second membrane and holster that you route the waste water line into the second membrane, then, the two production lines from each membrane is y to your di housing.. You will also require a higher capacity flow restrictor(150 to 200gpd). And, you will need a booster pump to up the pressure to 80-90psi. This route does produce a ton of useable water, but there is the added cost of the equipment, and, the second membrane of course isn't going to lat as long as the first.. But it really, really is the way if you want to produce a "lot" of water, or water extremely quickly..
I have done both, and can attest to how much water each does.. And actually, depending on your water pressure, you may just benefit from a booster pump.. Increasing the pressure(if yours is low), will make more water and actually make your membrane more efficient. Aquaticlife or at least a year ago, sold a nice little booster box.. It was silent, integrated auto flush, computerized, and you simply plugged the lines in.. I haven't checked lately, so I'm not sure if they still make them, but they were nice...
But those are basically your options, as the internals of the units hold all the same basic components.. It's just the type and brand that makes the difference(the best units have Dow membranes and Matrikx filters).. And you can add and subtract whatever you wish to a basic ro or ro/di unit.. My current unit started out as a simple 3 stage ro buddy 50gpd. Now, it's a seven stage 100gpd ro/di setup by adding components..
Sent from my SM-N910V using Tapatalk