It is the work horse filter of your Reverse Osmosis System. It reduces impurities from the water down to 1/1000 of a micron, reducing arsenic, lead, parasitic cysts, copper and more. All Water Filter Membranes should be changed every 2 to 3 years depending on the quality of your water. Also, check out our TDS Meter for testing your water. This will take out the guess work for when your Membrane needs to be changed.