Don't know about the price of the hydrologic system, but it is not really anything special. A standard three stage prefilter system with standard 10" cartridges. The RO membarne would have to be either a Dow FilmTech or an Applied membranes filter as they are the only manafcatures of standard home owner sized RO membranes rated at 100 gph that have a Rejection rate at a maximum 98%.
Actually it is a very minimal but good RO filter that is sold with a top quality RO membrane filter. I can almost guarantee the Filter Guys would sell you a better four stage filter with the same RO membrane for the same price. Here is the RO membrane. It is listed as a (98% rejection 100 gpd membrane). As you can see the 100 gpd best quality membrane is only $5 more than the best quality 75 gpd filter. So the cost fora four stge should be $141. That is obviously cheaper than the Hydrolic system and comes with three perfilters not just two.
http://www.thefilterguys.biz/ro_membranes.htm
As far as waste. They are all about 4 o to 5 gallons to waste for each gallon of RO water produced unless you put out be big bucks. the only other company that makes such ludicrous claims is SpectraPure and its system is over $1000 and has at least one pump annd other bells and whistles. It also does not perform as advertised. The Hydrologic still uses 4 to 5 gallons to waste for each gallon produced. Period. To do better than that you need extra pumps and/or divertor valves at a minimum.
here is no rocket science involved. Besides if you notice their ratings it is based upo water at a higher pressure and a hotter temperature than industry rating standards so the add is very deceptive as any other RO filters under those same parameters with the same RO membrane will perform exactly the same. A change in the color of the membarne housing is not going to change a membranes performance.
The industry has standards of testing just to prevent such deceptive advertising. A dealer can boost te inlet pressure and temperature even higher and then ck liam an even higher performing filter. My commercial RO filter has a 4" by 40" membarne and uses a 1 hp pump and a divertor valve and it still uses at laest 0.75 gallons of waste per each gallon of filtered water. It produces 100 gallons per hour. It sells retail for over $3500. I do not need that large of a system but I got it used very cheap, from a retail tropical fish store that went out of business. I use it to fill a 1000 gallon plastic water storage tank.
As far as an RO Filter producing water at a zero TDS. The very best commercial membranes are only rate at 98% minimum and 99% maximum. The very best home sized units are t arted at 96% minimum 98% maximum. If RO filters put out 100% pure water at zer TDS there would be no need to sell DI filters.
And no distilled water is not purer than RODI water. It is very difficult to obtain zero TDS water with even the best all galss laboratory distiller being operated/monitored constantly. Distiller are old technology and far from the best technology. Chemical manafacturers, hospitals, laboratories, electronics manafacturers and pharmecutical companies when they want ultra pure water use an RO filter and what is called nuclear grade DI resins, not distilled water.
In general if your TDS or conductivity meter says your RO water is zero ppm, then it needs recalibration. RO filters do not produce zero TDS water. If they did there would never be any reason for anyone to buy DI resin filters. Resins filters are used if you want zero ppm water because RO filters used alone (even with prefilters) will not provide it.
] = 3 ppm