Reverse Osmosis Additional Membrane Upgrade Kit You are purchasing a high-quality additional membrane kit for use with existing RO units. Adding an additional membrane to your set up can reduce the amount of waste water - as waste water from the current membrane is recycled and passes through the secondary membrane. This will reduce the waste water from your RO unit - which is ideal for saving money if you are on a water meter or wish to produce RO water quicker. Quick and simple to install!