BRS sells a good unit. You will get waste no matter which unit you use. Its usually a 4/1 ratio. You can get a water saver which runs the waste thru a second ro filter to save some of the waste water. RO units work best at 80+ pressure so if you have low water pressure get a booster pump.
So called water saver units are a bad idea unless you understand your water chemistry - especially your water hardness. Plumbing membranes in series without that knowledge is a bad approach. The MAXIMUM pressure that prefilter housings should ever see is something south of 80 psi. Filmtec membranes are spec'ed at 50 psi.
Don't fall into the trap of thinking that less concentrate (aka waste water) is always better. That's just not the way these things work.
Also realize you can adjust the amount of concentrate by changing out a little $4 part.