Reverse Osmosis Water Filters Buyer's Guide
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  We review, analyze and compare the best water filters in the industry including reverse osmosis systems, faucet filters, water distillers, pitcher filters, whole house filters, water softeners, shower filters, bottled waters and more.

How Does Reverse Osmosis Work?


membrane layersReverse osmosis (RO) is a popular form of water purification that is used by many people all over the world. The process by which a reverse osmosis system works and functions, however, is still a big mystery to many people. Even homeowners who personally installed their own systems and have enjoyed RO drinking water for years are often not completely sure of how the membrane filters work. For those who are interested in the mechanics, operations and technical functionalities of a reverse osmosis system, please read on.

Whether it’s a small 16” RO system installed under your kitchen counter or a massive warehouse sized city RO plant, the process used to purify water by reverse osmosis is the same. Modern thin-film composite (TFC) reverse osmosis membranes are created from sheets of synthetic polyamide layered with polysulfone and polyester support webs. Known commonly in the industry as leaves, multiple layers of these sheets are rolled together tightly over a permeate water delivery tube, and their layers form the cylindrical mesh through which contaminants are separated and filtered.

filtered water

Reverse osmosis membrane elements are housed in vessel chambers that are designed to separate the permeate treated water from the concentrate brine water. When pressurized water flows through the membrane, it channels in a spiral direction from the top surface sheets down towards the core center tube. The leaves of the membrane work as both a delivery path for the water and as a barrier for dissolved solids and contaminants. By the time the water is filtered down to the center tube, anywhere between 90-99% of the dissolved solids have been rejected and the potable quality water that flows out of the vessel can be stored in a separate tank or container.


To improve membrane performance and longevity, TFC elements incorporate a crossflow design that utilizes the existing water pressure and flow rate to rinse and clean the leaves during the filtration process. This feature helps keep the membrane fresh, clean and free from clogs and fouling, and this is what allows RO membranes to last a very long 4-5 years between replacements. Contaminants flushed from the membrane are carried out of the vessel on a separate line where it can be discarded as waste or collected for further processing.

The reverse osmosis membrane filtration process from start to finish may sound complicated and daunting, but the actual operation of these systems is usually very smooth, efficient and trouble-free. When installed and maintained properly with regular pre-filtration protection, reverse osmosis home systems will offer exceptional performance with very minimal upkeep and maintenance making it the ideal system for busy families that are looking for the best possible drinking water.