A good resource for home RO information is US Water Systems, the same folks we recommend for Stenner pumps.
Just to put some numbers on it - for a whole house RO system, you might get something like a 4,000 GPD RO setup. An RO system is typically spec'd to deliver 50% of the stated flow rate, so a system like that would theoretically deliver 2,000GPD. The base price for a system like that is currently listed around $8,000 not including installation costs. For municipal water like mine, I'd also need to add an active carbon backwashing pre filter to remove chlorine, chloramines, etc., as well as an anti-scale injection system (basically looks exactly like a chlorine stenner pump setup except it uses an anti-scale chemical). Finally, I would also likely need to do post-treatment calcite filter to raise CH and pH in order to not cause corrosion of pipes inside the home (it's not a good idea to have huge differences in mineral ion levels and pH between water in a pipe and water outside a pipe; it leads to galvanic corrosion). The addition of the pre- & post-treatment equipment would add about another $2,000 to the setup. One would also have to factor in the on-going costs of running the unit which include a variable-speed pump to send re-pressurized water back into the house plumbing, particle/sediment filter changes, anti-scale and calcite raw chemicals as well as any worn out Stenner tubes and UV disinfection lamps (the final stage of the RO injection is to run it through a UV lamp before going into the household plumbing to destroy viruses that may have made it through). One would also have to include (especially where I live as water is not cheap) the cost of all the waste water generated. For 2,000 gal system, one would have to assume that at least 15% of that value was generated in waste water, so something like 300+ gallons of water or 0.5CCF per day. If I'm operating at my peak water usage time where I hit the Tier 3 water charges, an extra 1/2 CCF per day is almost $4 to $6 per day added to my water bill.
One could theoretically tap off some of the water from before the final calcite filter to use an external water source. But you definitely want to limit usage in the pool as the system will only provide, at best, 2,000 gallons of water for all the days needs. The installation would cost about $10,000 worth of equipment and likely a few thousand dollars more for professional installation. While you would get a whole-house RO system out of the deal, I'm not sure it's worth the huge up-front cost unless you live in an area of the country where raw supply water is cheap.
See here for details -
US Water Heavy Duty Whole House Reverse Osmosis System