Most come with the extra faucet, so you don't get stuck using RO
water to wash your hands, wash dishes, etc.
There are different 'stages' you can get. a 2-unit piece may only be a carbon filter and an ro
membrane. or it may combine the membrane around the carbon filter, then have a secondary DI
phase. or a 3-piece would have all 3 split out and be the most filtering you can get.
Then you have output...10gallons per day? 50? The higher the value the higher the price.
is this for a SW
tank or FW
? Unless you have awful water, FW
should not need RO
. And before RO
, many, many many people kept SW
tanks without any problems. Point is, if nothing appears broken, don't start fixing...