The polymers have "pores" as small as down to 0.0005 micron in size. As a comparison, bacteria are in the region of one micron or a little bit less, virusesare 0.01 to 0.4 microns.

Reverse osmosis water purification filters (RO in short, or sometimes called hyperfiltration) is the best filtration available. It is filtration taken to the extreme level of singular molecules. Reverse osmosis water filters are typically used by the well known bottled water companies. It is a very efficient process of water filtering, it will remove more contaminants than any other method used for residential water treatment.

Reverse osmosis, also known as hyperfiltration, is the finest filtration available today. It is the most common treatment technology used by premium bottled water companies. It is effective in eliminating or substantially reducing a very wide array of contaminants, and of all technologies used to treat drinking water in residential applications, it has the greatest range of contaminant removal.

There are two types of reverse osmosis membranes commonly used in home water purification products: Thin Film Composite (TFC) and Cellulose Triacetate (CTA). TFC membranes have considerably higher rejection rates (they will filter out more contaminants) than a CTA membrane, however, they are more susceptible to degradation by chlorine. This is one of the reasons why it is important that a reverse osmosis system include quality activated carbon pre-filters.

A typical RO system is composed of an array of granular activated carbon (GAC) pre-filters, the reverse osmosis membrane, a storage tank, and a faucet to deliver the purified water to your countertop. Reverse osmosis systems vary in membrane quality, output capacity, and storage capacity.

What is a reverse-osmosis water filter?

A typical reverse osmosis filter system is something that sits under your sink, filtering out virtually everything but the pure water. Some models contain pre-filters to take out sediments before the RO membrane. These pre-filters must of course be changed every now and then in order for the water filtration to work smoothly.

In some cases it is also combined with an activated carbon water purifier to remove other substances, making it a perfect whole house water filtration system.

Reverse osmosis water purification - where to use?

A reverse osmosis filter is a good choice if what you want to remove is a wide spectrum of different contaminants like typically chemicals or heavy metals.

What will be removed with a RO water filter system?

A complete RO system with prefilter for sediment and a postfilter using carbon, strips out substances like heavy metals, lead, arsenic, copper, cadmium, chlorine, pesticides, salts, sulfates, nitrates and many other substances - virtually everything that could possibly contaminate your drinking water.

The reverse osmosis filtration system can also remove many bacteria and viruses. Some of these nasties can still get through though because if imperfections in the membrane so if these are your worry you should use other methods (as well) like ozone or ultra violet water filtration.

RO advantages, disadvantages?

A reverse osmosis system contains a 3-level barrier which few contaminants can penetrate, and does not need any electricity.

The main disadvantage is that it wastes 2-4 times the water it actually filters. If you try to make a system which has less waste - the membrane will have a shorter lifespan, since the waste water actually helps cleaining the membrane.

Installation of reverse osmosis filtration - difficult?

Not really, no. But most of us will need a plumber still.

How much does it cost?

Typically a few hundred dollars or more for the system and then you need to replace the membrane every 2-3 years. Expect a cost around 5-10 cents per gallon for filtered water.