The different stages inside a residential Reverse Osmosis system
Domestic and commercial reverse osmosis water treatment system in general, is actually refering to a series of
carefully selected water treatment methods used in combinations to achieve the best possible quality in supply
water. The diagram on the left shows the general schematic of a typical 5 stage RO water system.
Stage 1
The systems begins with normally a 1 to 5 micron sediment filters to hold back any large particulates including
large iron slits, dust, turbidity. This will prevent any deposition of large particles onto the ultra fine RO
membranes which typically in the order of 1 to 100 angstrom (1 angstrom = 1/10,000 micron or
1/10,000,000,000 meter of 1/10trillionth meter, this compare to human hair thickness with average diameter of
approximately 750,000 angstrom or 75 micron).
Stage 2
The Granular Carbon filter is then use to pick up about 90 to 95% of all the organic particles and remove the
majority of chlorine in the water stream. Under proper maintenance, the carbon filter will help to maintain the
efficiency of RO system for longer service life.
Stage 3
The Block Carbon filter is then use to pick up about 90 to 95% of all the organic particles and remove the
majority of chlorine in the water stream. The carbon filter can completely remove bad smell in water. Under
proper maintenance, the carbon filter will help to maintain the efficiency of RO system for longer service life.
Stage 4
Then the fourth step is the use of RO which is the heart of the system. The fine membrane as explain by previous
article regarding the Reverse Osmosis. It acts as surface filter with fine enough mesh to pass only a small
amount of minerals and water molecules. Any long chain organic compound, including micro-organisms and also
artificial compounds such as pesticide and weedicide will be screen out. Because of the ultra fine mesh size of
the membrane, it will also block all harmful virus and other micro-organisms which may pass through in case of
alternative filtration technology. Storage Tank
Because of the high pressure drop of the Reverse Osmosis process in order to filter the water particles, the
clean water stream has very slow flow rate and a temporary water reservoir tank is used to buffer the flow when
no clean water is draw from the system. The clean water is collected in the tank when the system is in idle status
and also the tank will act as a pressure buffer to smooth out any pressure changes between the two side of
reverse osmosis membrane which will extend its life. A automatic shut off valve (whether it is a electronic or
mechanical) is then used to shut off water supply to the RO system when the water tank is full.
Stage5
There are sometimes small odors in the clean water which is a result of the interior finishing of the water tank
and inner lining of the tubing. Thus a final post carbon filter is normally added as a final polish filter to remove
such odors or taste and to give the great taste typical of spring water.
It is common for the sediment and the first carbon pre-filter to plug up and efficiency reduced by the end of
service life cycle and the second carbon filter has thus little effect to the overall performance of the system.
While adding a second activated carbon pre-filter to the system has no ill effect to the drinking water quality, the
use of such system may be subject to the water source conditions including chlorine concentration, organic
content (such as the case of having a no-pretreat surface water source), etc. and thus it is best to talk to your
Perfect Life Water specialty agent for recommendation first.