Filtration, carbon filtration and oxidation are well-established methods of conditioning or treating water, so I will further assume that you are referring to the plethora of companies who are promoting “salt-free water conditioners.” I will say that there is some validity to most of these methods, however companies or websites who say that they “soften” water without salt or make other prespoterous claims like “salt can be absorbed through the skin” or that electronic devices increase sudzing are not dealing in reality and should not be trusted.
In my thirty-plus years of experience, I have personally tried every method known to man to remove iron. Today, I primarily tried use hydrogen peroxide, as it is a much better oxidizer of iron than either chlorine or potassium permanganate and does not leave excess air in the water like oxygen systems. Unlike chlorine, hydrogen peroxide is simply hydrogen and oxygen and produces no harmful chlorination byproducts. A hydrogen peroxide system consists of a chemical injection pump, solution tank, in-line static mixer, and a backwashing filter to remove the oxidized iron.
Sizing a reverse osmosis system is critical when you have multiple outlets, especially if one or more is an under-the-counter ice-maker. Most residential reverse osmosis systems are 24 to 50 GPD (gallons per day), which is not nearly enough for such an ice-maker. Additionally, production is reduced whenever the water temperature is below 77 degrees F, and whenever the pressure is below 60 PSI. In the real world, a 50 GPD reverse osmosis system in the Midwest may produce 20-25 GPD, when the demand may be up to 150 GPD
Carbon filtration is a marvelous method for removing chlorine, chemicals, pesticides and numerous other contaminants, providing it is applied properly. For example, you would not want to put a carbon filter on water that is microbiologically unsafe. This would require chlorination (with adequate contact time) ahead of the carbon filter, or some other method such as ultraviolet or ozonation to inactivate the bacteria.
Also, did the salesperson leave literature about his product? Does it use the word “purified” in it? There are some salespeople who make all kinds of claims in the home, but leave no literature to back their claims, and they fail to put anything in writing. While there is no rule of thumb as to what a water treatment system should cost (it really depends on what YOUR water is like and how much you should clean it up), generally it should be less than $2,500-usually a lot less in most areas, unless there are extraordinary installation considerations or unusual water problems.
In times past, most RO systems were rated at 12 to 50 gallons per day. That simply means that if it ran continuously for 24 hours it would produce that amount of water. However, in the Midwest where water temperatures are lower than 77 degrees Fahrenheit; the production is about half the rated capacity of the system. Today, many homeowners are opting to connect their kitchen sink, vegetable sink, pot filler, wet bar, multiple ice-makers and the master bath to the RO system. This necessitates the usage of higher capacity RO systems (75 to 300 GPD) along with larger storage tanks and delivery pumps, which boost the pressure.