What Are the Filter Stages in a Reverse Osmosis System?
Written by: Alexandra Uta // Last Updated: Aug 29, 2023
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A reverse osmosis system is a multi-step filtration system that is one of the most effective for providing you with almost 100% pure water.
There are various filter stages in any system, but what they are and how many varies depending on your individual setup.
Let’s look into it a little more.
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Key Takeaways
- All reverse osmosis systems as a base will have a carbon pre-filter, the RO membrane, and a carbon post-filter.
- 4 and 5-stage and up RO systems will also have a sediment pre-filter and possibly extra filtration steps such as a UV purifier or remineralization filter.
What Are the Filter Stages in a Reverse Osmosis System?
So, what are the filter stages in a reverse osmosis system?
Depending on your setup, you can find various filter media in your RO system. The most likely filter stages you will come across include:
Sediment Pre-Filters
To prevent the reverse osmosis membrane clogging, sediment pre-filters play a critical role in eliminating larger particles floating in your water, such as sand, rust, dirt, and debris.
Activated Carbon Pre-Filters
Activated carbon is a necessary step in all reverse osmosis filtration systems. Its primary function is to filter out chlorine to prevent it from damaging the RO membrane.
Reverse Osmosis Membrane
The other primary component you will find in any RO system is, of course, the reverse osmosis membrane. This is responsible for the majority of the water purification process. It eliminates a wide range of contaminants; however, its efficiency can be impacted by chlorine in the water, hence the need for prior removal.
Activated Carbon Post-Filters
A post-filter with activated carbon is often utilized after the water leaves the RO storage tank. This will give the water a final polish, eliminating any odors picked up from sitting in the tank.
Specialized Filter Stages
Then, there could be various special filter stages. The most common are:
- Remineralization filter: This filter returns any essential minerals removed from the water by the RO membrane.
- Ultra-violet (UV) filter: This will help to eliminate any remaining bacteria or other microorganisms in the water.
3-Stage Reverse Osmosis Systems
A 3-stage reverse osmosis (RO) system consists of three filtration stages to ensure high-quality water purification:
- Carbon Pre-Filter – The first stage employs a carbon pre-filter, available in either granular activated carbon or carbon block form. Its primary purpose is to eliminate elements like chlorine. This pre-filtration process helps protect the integrity of the RO membrane.
- RO Membrane – This crucial component effectively removes dissolved solids, heavy metals, and other harmful contaminants, ensuring the purity and safety of the water.
- Carbon Post-Filter – The third stage provides a secondary activated carbon post-filter that further enhances water purification and taste.
Further Reading:
4-Stage Reverse Osmosis Systems
Most 4-stage reverse osmosis systems will have the same stages as the 3-stage, but with an added sediment prefilter, so:
- Sediment Pre-Filter – The sediment filter eliminates larger particles of dirt, debris, and dust, preventing any obstruction to the RO membrane stage.
- Carbon Pre-Filter
- RO Membrane
- Post Carbon-Filter
5-Stage Reverse Osmosis Systems
A 5-stage RO system for water purification will usually contain the same components as a 4-stage, plus one extra step. This extra step could be various things, such as an additional carbon filter, a remineralization filter, or an extra sediment filter for water with a lot of debris. It could look something like:
- Sediment pre-filter
- Sediment pre-filter
- Carbon pre-filter
- RO membrane
- Carbon post-filter
Or:
- Sediment pre-filter
- Carbon pre-filter
- RO membrane
- Carbon post-filter
- Remineralization filter
And various other combinations.
Are More Filter Stages Better?
When selecting the ideal number of filter stages for a reverse osmosis system – be it 3, 4, 5, or more – the answer really depends on what needs filtering in your particular water and how contaminated it is. Some systems have extra filtration steps added that may sound impressive but will not make any actual difference to your water. Merely having more stages does not guarantee superior results.
While additional filter stages have the potential to improve contaminant reduction, repeating the same media consecutively might be useless for you. Therefore, it is best to evaluate your water quality to determine the optimal number of filtration stages needed and which ones.
What’s the Bare Minimum Required?
At a bare minimum, a reverse osmosis system should have a carbon pre-filter, the reverse osmosis membrane, and carbon post-treatment.
If you have any questions about RO system stages please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
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