What is a Reverse Osmosis Water Filter?

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  • Written By: Dan Blacharski
  • Edited By: L. S. Wynn
  • Last Modified Date: 08 March 2020
  • Copyright Protected:
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Those who are concerned about pure water, and want to have a constant source of water free from contaminants may wish to install a reverse osmosis water filter. Reverse osmosis is also known as hyper-filtration, and is the most thorough type of filtration available. Although water filtration is the most common usage, reverse osmosis is also used to purify other liquids such as ethanol and glycol.

The reverse osmosis water filter can remove particles as small as dissolved ions from the water supply. It stops virtually every contaminant. Typically, there are at least three stages in a reverse osmosis filter. Water is first forced through a small prefilter, which strains out sediment, and then it is passed through a membrane to screen out smaller contaminants. The last phase is a carbon filter. Between these three elements, the reverse osmosis water filter will eliminate a wide variety of contaminants, including minerals, bacteria and viruses, and provide a constant supply of fresh, clean water at low cost.

The reverse osmosis water filter uses a mechanical process that does not require a power source. One drawback is that at least two gallons of tap water is wasted for every gallon that is filtered. The rejected water serves a purpose though, this is what keeps the unit's membrane clean. A reverse osmosis water filter can be installed by any competent do-it-yourselfer in an hour or two, although some may prefer to have a plumber handle the installation.


To understand a reverse osmosis water filter, you must first understand osmosis. When there are two different liquids, separated by a semi-permeable membrane, water passes through the membrane towards the more concentrated solution, thus diluting it. This is the osmosis process.

If pressure is applied to the side that is more concentrated however, the process can be reversed. In the latter case, the contaminants on the concentrated side do not pass through to the less concentrated side, but instead are separated out and cleansed away. Through this process, the dissolved solids are separated from pure water. The membrane itself stays clean as a result of the crossflow. Liquid that does not pass through the membrane continues in the downstream direction, and cleanses the particles from the membrane.



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what are the treatments for the reverse osmosis rejected water?

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