How does a reverse osmosis system work to purify water?

Reverse Osmosis Water System

A reverse osmosis water purifying system at work. Flickr Commons image via StickerGiant

My husband and I recently purchased a reverse osmosis system for our drinking water. The system came from Lowe’s and cost relatively little money. The installation process took about two hours total and then another 24 hours of waiting before it had stored enough water to use. 

Problems Solved by a Reverse Osmosis (RO) Water System

While reading the documentation on our particular system I was surprised that the system claims to rid household drinking water of just about every impurity imaginable. From chemicals like Chlorine and Trihalomethanes, BPA and pharmaceuticals, to metals such as Lead, Radium, and Arsenic and solids including Nitrites/Nitrates and Asbestos. Finally, the system removes viruses and bacteria like e.coli, Norovirus and Rotavirus. In addition, this $169 gem of a machine sitting nicely underneath my kitchen sink, remineralizes my drinking water and balances the pH before sending out a neat stream of cool water from it’s own little faucet.

I thought it all sounded pretty amazing. I mean, I realized this was possible and even vaguely knew that it happens on an industrial level however, the idea that I could go from drinking water with all of these contaminants, to having the peace of mind that comes from knowing each of those items listed had been removed in one afternoon got me pretty excited. I really wanted to know how this thing works.

Here is what I found: 

How it Works

A Reverse Osmosis (RO) System is the most trusted way to purify just about any sort of water.

RO is even used on Navy vessels to turn seawater into potable drinking water. 

In broad terms the system works by forcing pressurized water through a series of filtration devices. Each filter gets increasingly finer and therefore capable of filtering out increasingly smaller particulate from the water.

Tanks in a Reverse Omosis System

Tanks in a reverse osmosis water system. Flickr Commons image via Franklin Dattein

Levels of Filtration 

The first level of filtration is a flat sheet of polyester fiber support base. On top of that is a layer of polysulfone with micro pores. A polyamide layer of .2 micron width is the last layer of the membrane. In other words, all of that is one sheet. 

Multiple membrane sheets are layered on top of one another with feed channel spacers between them and lastly a layer of permeate spacer to help the water flow evenly through the membrane layers. All these sheets are sealed together and rolled up (think jelly roll or toilet paper roll. I prefer jelly rolls, but I digress). 

Seven sections of the “jelly rolls” are connected and wrapped together into one long pipe. As the water is forced through the length of the rolled up filter it travels in a spiral formation. As the water spirals the filters remove increasingly smaller particles from the water and force it through the very center of the filter before storing it in a tank. After the storage phase the water goes through one more filtration level to remove any trace odor present in the storage tank.

The Leftover Water

Meanwhile, the contaminated water is exiting the other end of the system simultaneous to the purified water becoming cleaner. The “concentrate” or dirty leftover water gets recycled to produce more clean drinking water the next time around. RO systems are so meticulously pure that they even get a separate faucet which acts as one last guarantee that what is coming out is as pure as the driven snow (purer than that, even)

Reverse Osmosis Water Filter Faucet Image

Most reverse osmosis water systems get their own faucet. Flickr Commons image via Justin Henry


My conclusion to this whole process has been to recommend these filtration systems to everyone I know. These systems seem like an excellent option regardless of what sort of contaminate you may be trying to address in your water. I would also recommend RO to those 

like me, who were not exactly sure what could be lurking in their drinking water. For home and industrial systems alike RO seems to be the gold standard for filtering water. As a homeowner I am also glad to know that these systems are often able to be hooked up to an ice machine or a refrigerator to give you the freshest, most pure and deliciously cold drinking water available. Enjoy.

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