Reverse Osmosis is simply one of the most reliable and effective methods of purifying water used today. It offers a more advanced water treatment process than entry-level pour-through pitchers or carbon filtration.
RO systems filter almost every contaminant present in your water, ensuring that it’s safe for drinking and cooking.
Each system features different types of filters for excellent results. It also uses the osmotic membrane, a very effective filtration technology, which removes the tiniest and most stubborn contaminants.
Different types of reverse osmosis systems are available today with varying number of filtration stages.
In fact, the number of stages in an RO system has become one of the industry jargons in proving the superiority of a system or the quality of water it produces.
Is this really true? Or just a marketing gimmick for companies trying to sell you more features than you need? Keep on reading, and you’ll get the answer soon enough.
What's in this Guide?
What Does Each Stage of RO Filtration Do?
A standard reverse osmosis system filters water in 3 stages: sediment, carbon, and reverse Osmosis. Each stage plays an important role independently and compliments others to achieve the best water filtration results.
Sediment filtration, which is usually the 1st stage, removes large particles, rust, dust, and dirt from the water. By getting rid of these particles, this stage helps to protect the reverse osmosis membrane.
Carbon filtration is the next stage. Here, chlorine, chloramines, VOCs, odors, colors, and cloudiness are absorbed before the water goes into the next stage.
Reverse Osmosis is the final stage and the core of the entire system. In this stage, water is pushed through a semipermeable membrane with a rated pore size of 0.0001 microns.
The RO membrane removes up to 99% of all impurities present in the water.
5-Stage Reverse Osmosis System
A 5-stage RO system filters water in 5 stages.
5-Stage Reverse Osmosis Structure
- Sediment pre-filter: A sediment pre-filter removes sand, silt, dirt, rust, and larger particles from the water.
- Carbon pre-filter: An activated carbon pre-filter eliminates elements that leave an unpleasant taste and smell in the water, including chlorine.
- 2nd carbon pre-filter: Another activated carbon pre-filter eliminates all odor elements and bad tastes from the water.
For the 2nd and 3rd stages, most systems use either 2 of the same carbon block in the 2nd and 3rd stage or a granular activated carbon pre-filter on the second stage and a carbon block pre-filter in the 3rd stage.
- RO membrane: The reverse osmosis membrane removes the most stubborn contaminants like lead, arsenic, and nitrates from the water.
- Carbon post-filter: A carbon post-filter provides final polishing of the RO water before it’s delivered to the faucet.
7-Stage Reverse Osmosis System
7 stage with remineralization filter
7 stage with UV
A 7-stage RO system filters water in 7 stages. Each stage is designed to eliminate contaminants and progressively improve the water’s quality.
7-Stage Reverse Osmosis Structure
- Sediment pre-filter: A sediment pre-filter removes sand, silt, dust, dirt, rust, and other large particles from the water.
- Carbon GAC pre-filter: A carbon granular activated pre-filter eliminates bad odors and tastes from the water.
- Carbon block pre-filter: A carbon block pre-filter gets rid of chlorine, chloramines, cloudiness, colors, bad tastes, and odor from the water.
- RO membrane: The RO membrane removes contaminants down to 0.0001 microns.
- Fine GAC filter: A fine GAC post-filter provides final polishing by removing any lingering tastes and odors from the water.
- Alkaline remineralization filter: An alkaline remineralization filter restores essential minerals into the water raising its alkaline level to 7.5. It also makes the water tasty.
- UV stage: The UV light helps eliminate all microorganisms from the water, including bacteria, viruses, and cysts.
Why Add More Stages After Reverse Osmosis?
Reverse osmosis water is flavorless, the reason why most people don’t like drinking it. Adding a post filter (coconut shell carbon filter) helps remove any residual tastes and odor from the water.
Some systems come with a remineralization filter that adds essential minerals to the water, making it tasty.
Are 7 Water Filtration Stages Better than 5?
7 stages are better than 5 because of the alkaline remineralization filter and the UV stage. If a 5-stage system doesn’t have a remineralization filter, the water won’t have essential minerals and hence be less healthy.
A remineralization filter also makes the water tasty.
Most 7-stage RO systems also feature a UV stage. This is the only water filtration stage that helps to remove microorganisms such as bacteria and viruses from the water.
In this stage, living microorganisms in the water are exposed to UV light, which attacks and destroys their DNA.
Although both 5 and 7-stage RO systems help filter and purify water for drinking and cooking, a 7-stage works better.
But that’s only if the 2 added stages offer more benefits.
Therefore, when ready to invest in a reverse osmosis system, look closely at what you’re buying to verify whether you really need it.