How much does a good RODI system cost and how much water does it "waste"?

Question

how many gallons of water does the system need to filter to get one gallon of reverse osmosis deionized water?

Answer 1

A commercial one that could provide municipal water wastes 100 times as much incoming water as goes out. So your 1 gallon of potable water would take 100 gallons of brackish water incoming.

The systems that yield a sizable amount of water are incredibly expensive including the replacement filters and the skilled workers to run it successfully. It is a great solution if you have lots of brackish water but the yield will not come cheap.  I don't have the nubmbers in front of me but they move RO out of the casual category into the "I better have a good reason for going that way" category.

If you were on  a coast like the Gulf of Mexico where a well that yielded good water was impossible but you had an unlimited supply of brackish it would be worth your doing an analysis. Most other water seekers start with surface or aquifer water..