All ro units produce waste unless tou want to spend mega mega bucks.
However some produce a lot less waste, I have a 40/40 ro with a booster pump that I got from purewindowwater.co.uk. My tap water is 400ppm tds and it brings it down to 2ppm tds. The ratio of pure to waste is 1L pure .8L waste. It was price though well over grand.
Other ro units will produce pure water with a lot more waste or water thats not as pure and they will probably be a lot slower.
Simon