eesmaker, and Big Al,
Most if not all 100gpd units Ro membrane are pnly 90% rejection rate which means you will use up your DI resin faster, a lesser GPD unit Ro membrane is 96-98% rejection rate, example, Your inlet TDS's are 500, a 100gpd at 90% rejection rate gives you 50 TDS's for your DI resin to clean up. lets take the average of 97% of the lesser units, that is 15 TDS's for your DI resin to clean up. it will last 3 times longer, and Di resin is expensive. Plus RO membranes are rated at 60psi at 77*F water anything less in any combo will lower production water, anything higher in any combo will increase it. go with a 50-75gpd unit.Give me a temp, presure, and source water TDS and I will give you calculators to figure out how much water per day for your unit.