RO Unit newb questions

[Myka]

RO cartridges are only so effective:

Filmtec 50 gpd = 98% rejection rate
Filmtec 75 gpd = 98%
Filmtec 100 gpd = 90%
BFS 150 gpd = 98%

So that means if your tap water is 100 tds, then with a 50 gpd unit your product water will still have 2 ppm tds. That's not good enough. The DI resin will take that 2, and turn it into a 0. IMHO, it is imperative to have 0 tds product water which is why you buy a TDS meter as well, and be sure that your unit is working properly.

Find out the rejection rate on the eBay units before you buy. If you're handy, you can buy a 4 stage RO unit on eBay as long as it has three canisters and the RO. Rerun the hoses, and replace the last one with a DI resin cartridge. Just as long as the order the water travels is micron filter, carbon block, RO, DI. Be sure that the flow restrictor rating is the same as your RO cartridge, and that it's placed inline after the RO cartridge.