Up to 90% is used and average results range from 70-80% range. This is due to a lot of variables with type and size of RO tank, water pressure, output of membrane, etc.Regular auto shut off valves will turn off the water feeding the RO system when the tank pressure reaches 60% of the incoming water pressure. When using a permeate pump, the work of feeding the tank has been eliminated. So you can put more water in the tank efficiently. That means you can use the 90% valve which will let the tank fill until it reaches 90% of the incoming water pressure. More water in the tank means more pressure at the faucet or ice maker. Only recommended for use with a pump like the permeate pump for best performance. Connects easily with 1/4" quick connect fittings. Comes with an instruction sheet showing you how to connect to your RO system.