I'm lazy...the following is a cut and paste...I think you should be looking for a 4:1 ratio though, 4 parts waste to every 1 part of good water. If you're getting more good water to waste, I would say something is wrong with your filter...at least that's what me thinks
"The RO stands for Reverse Osmosis and refers to the chemical/mechanical method of filtering the water. Basically the water is forced through a semi-permeable membrane that allows water molecules through, but blocks most other organic and inorganic materials. This can only happen with a pressure differential from one side of the membrane to another. But the membrane is very delicate and would burst if presented with the normall pressures a normal filter cartridge endures. Thus the water flows across the membrane with only a moderate differential pressure. The second reason for the waste water is that since the pores in the membrane are very small, they clog easily. The flowing water across the membrane also flushes the membrane clean. Even so, most RO units have a method of flushing the membrane with full flow to clean it further."