Comparing filtration with reverse osmosis is like comparing two brothers with almost the same features, only with different ages perhaps. This is because the principle used by both systems is the same – filtering sediments out of the water.
Let us look first into reverse osmosis.
Reverse osmosis
Because of its present capacity of filtering some of the minutest substances on earth, the process of reverse osmosis is sometimes called hyper filtration. It allows the removal of particles as small as ions from a liquid solution.
The most common use for reverse osmosis process is in purifying water. It is used to remove salts and other impurities to restore the water’s color, taste, and its other properties.
The process is also used to purify other fluids such as ethanol and glycol by removing their contaminants and purify them for better functions.
The heart of the reverse osmosis process is the semi-permeable membrane that allows the fluid being purified to pass through while blocking the contaminants.
Another vital requirement to the system is the driving force that pushes the liquid through the membrane. The most common device used is a pump. The stronger the pressure needed, the bigger the driving force should be.
Nowadays, most reverse osmosis processes now incorporates the use of crossflow, the additional process where the membranes clean themselves during the operations.
As some of the fluid passes through the membrane the rest continues downstream, sweeping the rejected species away from the membrane.
To date, reverse osmosis is capable of straining bacteria, salts, sugars, proteins, particles, dyes, and other chemical constituents.
Filtration - How does it work?
Filtration involves water flowing through a granular bed of sand (or any other suitable filtering medium) at a low speed. The action permits the filtering media to retain most solid materials while permitting water to pass through.
To ensure adequate removal of unwanted particles, the process of filtration is usually repeated. This process is generally known as slow sand filtration. It is the oldest method of filtration but still in use up to this day.
The more modern filtration systems today use carbon as the filtering medium. The carbon is compressed into solid blocks. (This is in direct contrast to the old loose granular sand filters of old.) The carbon filters in solid blocks often include other media substances, and called multimedia filters. This new type of filter works together and in both ways, chemically and physically.
Physically, it duplicates the old work of the slow sand filters: blocking the passage of unwanted materials with molecular structures larger than that of water.
Chemically, it does additional work by the process of absorption. With it, the atomic charge of the carbon and other media encourages unwanted particles to abandon their bond with the water and attach themselves to the filter. The other media included in the filter are designed for more particles to bond with it.
Water is then directed to several stages of carbon and multimedia filters to ensure removal of more unwanted materials. The first removes the most concentrated chemicals (chlorine, etc.) and the other next stages are for the removal of smaller and more hard-to-get chemicals like pesticides.
Some notes on reverse osmosis and filtration
Carbon and multimedia filters possess the same purifying capabilities as reverse osmosis and distillation. All three – filtration, distillation, and reverse osmosis – are all able to remove dangerous chemicals.
The slow process of carbon and multimedia filters does not need expensive energy sources like distillation (heat) and reverse osmosis (force pump), thereby making it cost-effective. It wastes little water in the process, too.
Again, when comparing filtration with reverse osmosis, the issue might all boil down again to cost-effectiveness in maintenance and ownership of either of these water-purifying systems.
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There are actually a few methods to choose from when looking to turn hard water (with minerals and other solids) soft (without.) The most common is a combination method of carbon filter along with a secondary sub-particle filter or ion exchange. These filters can produce water just as inexpensively and conveniently as reverse osmosis filters while leaving the trace minerals your body uses for nutrients.
There is debate from either side of the drinking water debate as to whether the amount of minerals in carbon filtered water are enough to impact a persons 
