When compared to the RD-102, based on the link the RD-106 comes with a 4gal pressure tank (and the photo displays one less DI
resin stage, though the write up depicts two).
Optimally, (excluding the RO
membrane housing) you'll want to go with all vertical housings to avoid any potential media by-pass (the DI
stages in the watergeneral link have horizontal DI
stages). The vertical housings also hold a greater resin capacity (visually it appears that one vertical DI
housing holds more resin that two horizontal DI
Just going by the ratings that are listed on their link I would go with a unit that has a RO
membrane with a higher rejection rate. They list rejection rates of 95%-97%.
The BRS unit that dimdim referenced is equipped with a 75gpd Dow Filmtec membrane which offers a 98% rejection rating which out-performs the watergeneral units. (From what I understand, higher gpd results in lower rejection rates).
I personally use an Ultra-High Rejection Spectrapure membrane which rejection over 99% of the TDS
from my tap water (tap water 259ppm, RO
water 1ppm, RO
The water general dual DI
stages will still provide 0ppm RO
water product water, however the lower rejection rates offered combined with lower resin capacity will result in a higher rate of DI
For a unit approximately costing $150 I'd go with any of these three:
5-stage $160 RO
unit from TheFilterGuys:
5-stage $159.99 RO
unit from BRS:
BRS 5 Stage RO/DI System - 75GPD - Bulk Reef Supply
5-stage $169.99 RO
unit from PurelyH2O:
(the Filter Guys & BRS 5 stage unit comes with 2 carbon blocks, while the Purely H2O 5 stage unit comes with 2 vertical DI
stages). For water containing high chlorine or chloramine levels you may want to go with dual carbon blocks over dual DI
Whatever unit you go with, for the most part they're interchangeable when it comes time to replace filters or membranes (if the housing are of the same horizontal/vertical orientation). Membrane change outs (if going from a 100gpd to a 75gpd as an example, may require a flow restrictor change out).