I purchased a Water General RO/DI system off of Ebay several years ago. It worked adequately for several months, but I was not completely satisfied with it until I had made a couple of modifications to it that brought the price up to the same range as I would have paid had I purchased a system from one of our sponsors.
First: I changed out was the horizontally mounted DI filter. The reason for this is that ALL DI resin will shrink as it is used. On a horizontal mounted filter this leaves a channel at the top of the filter where the water will flow with little or no contact with the DI resin (path of least resistance). The DI resin will shrink on a vertically mounted filter as well, but the water must still flow through the resin from the bottom before reaching the gap at the top. Second the DI filter that comes with this unit is about half the size of a standard filter, which means exhausting the resin faster and more frequent changeouts of the resin. I went with a full size filter housing mounted vertically and could not be happier with the performance.
Second: I swapped the 110 gpd RO membrane for a 75 gpd membrane. The 100 - 110 gpd membranes have a 90% rejection rate, where as the 75 gpd membranes have a 95 - 98% rejection rate. This allows the DI resin to not have to work as hard to remove the remaining TDS.
Third: If you purchase this system you will probably want to replace the second Carbon filter with Catalytic Granual Activated Carbon. Regular carbon filters will remove chlorine, but not chloramines, which almost all of the Houston area municipalities are now using. Without this the chloramines will have to be removed by your RO membrane (the most expensive filter) and will greatly reduce its lifespan.
I used:
http://www.buckeyefieldsupply.com for my upgrades, and wish that I had just purchased a system from them from the begining.
JMO
Don
