Reverse Osmosis = This is a purification method for tap-water. Prefiltered tap water is pushed through a reverse osmosis membrane. Water that makes it through is considered pure, while water that does not, is sent through a special tube and is rendered impure. As it relies on water which is able to pass through the membrane, it also generates a large quantity of "waste" water which cannot be used. This is one of the best, but slowest methods of tap water purification.
What constitutes a Unit? - As you can see in the above photo, an RO/DI unit can consist of several chambers, each of which performs a filtering method. Depending on the models purchased, they can come with any number of "stages", some units even have UV stages for sterilization, but for our purposes, a simple "home use" unit will do just fine. As such, I would buy a unit that has at least the following four stages built into it. Sediment Filter - Removes the largest particles from the water, which helps to prevent the finer filters next in line from becoming clogged with material. Carbon Filter - Removes by adsorbtion dissolved organics and chlorines which would damage the reverse osmosis membrane. Reverse Osmosis Membrane - The actual membrane that allows only certain sized molecules to pass through it. While it does a good job of purifying the water, it does allow compounds / molecules of substances that should be removed, which is where the dionizing filter comes into play.Dionizing Cartridge - Contains a resin which adsorbs those elements that were small enough to pass through the RO membrane with the water molecules.
Used by permission. Many thanks to Charlies and Linda Raabe for their support. www.chucksaddiction.com