3-Stage vs 5-Stage Reverse Osmosis Systems
Written by: Gene Fitzgerald // Last Updated: Aug 14, 2023
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A 3-stage reverse osmosis system can already produce clean and pure drinking water.
So how powerful must a 5-stage RO system be? Or are 5 filter stages in a reverse osmosis system unnecessary?
3-stage vs 5-stage RO system, which one should you go for? Let’s find out!
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Key Takeaways
- A 3-stage reverse osmosis system usually has a carbon pre-filter, an RO membrane and a carbon post-filter.
- A 5-stage system simply means it has 5 filtration stages, but they can be in various arrangements and combinations. 5-stage systems can include sediment and carbon pre-filters, the RO membrane, carbon post-filters, and possibly remineralization or UV.
- Which decision which exact setup to choose should be based on your water quality.
Difference Between 3-Stage and 5-Stage Reverse Osmosis Systems (Structure & Application)
3 stage reverse osmosis systems and 5-stage reverse osmosis systems vary in structure and application. For many, a 3-stage system is ample, but some water sources or personal preferences may negate a more comprehensive 5-stage system…
3-Stage Reverse Osmosis Systems
The typical 3-stage RO system consists of several filter components.
- First, there is the carbon pre-filter in either granular activated carbon or carbon block form. Its purpose is to get rid of any bad tastes and odors in water, such as chlorine, and ensure the integrity of the RO membrane.
- The RO membrane is the second (and key) element of a reverse osmosis filtration system, eliminating dissolved solids and other hazardous contaminants like heavy metals.
- The third stage involves the carbon post-filter, which acts as a secondary activated carbon filter, further enhancing the water’s taste and odor.
Some variations on a 3-stage system may include a carbon and sediment combination pre-filter, making it a 4-stage system, according to some.
5-Stage Reverse Osmosis Systems
You can use various combinations of filter stages in a 5-stage RO system. They include:
- 3 pre-filters (2x sediment + 1x carbon), RO membrane, carbon post-filter.
- 3 pre-filters (1x sediment + 2x carbon), RO membrane, carbon post-filter.
- 2 pre-filters (1x sediment + 1x carbon), RO membrane, carbon post-filter, remineralization filter.
- 2 pre-filters (1x sediment + 1x carbon), RO membrane, carbon post-filter, UV lamp.
So, a setup might look like this:
- Sediment pre-filter: Screens out larger dirt/debris particles and other smaller particles.
- Carbon pre-filter: Reduces elements such as chlorine and other contaminants that cause bad tastes and smells in the water. Also targets all kinds of organics.
- 2nd carbon pre-filter: Further reduces elements organic chemicals.
- RO membrane: Primarily filters out dissolved solids, such as lead, arsenic, fluoride, nitrates, etc.
- Polishing filter: Provides ‘polished’ water through activated carbon filtration.
About the Different Filter Stages in Reverse Osmosis
Depending on the setup you have and what kind of filter components and add-ons you choose for your RO system, you are likely to encounter the following:
Sediment Pre-Filters
Sediment filtration plays a crucial role in water purification by removing debris from the water. Placed at the beginning of the filtration process, it captures larger particles, which helps the subsequent steps to better target other contaminants that may sneak past sediment filtration.
Think of it as giving the rest of the system a helping hand in effectively filtering the more minute substances without clogging from dirt.
Carbon Pre-Filters
In a carbon filtration stage, water flows through the carbon, effectively removing tastes, odors, cloudiness, colors, and chemicals such as volatile organic compounds (VOCs), chlorine, and chloramines. This eliminates most taste commonly found in municipal water.
It is also important to get rid of chlorine before the water reaches the delicate reverse osmosis membrane in order to avoid damage.
RO Membrane
In this crucial phase, water flows through a semipermeable membrane containing pores as tiny as 0.0001 microns. An impressive 99% of impurities and contaminants are successfully removed from the water.
Carbon Post-Filters
Integrating a carbon post-filter eliminates any lingering taste or smell making the water more polished. This is often used after storing the purified water in a tank.
Remineralizer
Following reverse osmosis, water is often perceived as flavorless or ‘flat’.
A remineralization filter is a post-filtration step that returns natural minerals like calcium and magnesium to the water in a balanced fashion. This gives the water a slightly mineralized taste while raising its pH, which some people prefer.
UV Purifier
A UV purifier is a stage that can be added to an RO system that is useful if the feed water has microorganisms like bacteria and viruses. This stage uses ultraviolet light to kill pathogens in the water and stop them from reproducing.
3-Stage vs 5-Stage Reverse Osmosis System – Which Is Better?
So, 3-stage vs 5-stage reverse osmosis system, which one is better?
One is not necessarily better than the other. The quantity of filter stages required varies based on water quality. If you’re dealing with significant contamination or various types of contaminants needing different filter methods, a higher number of filter stages is often necessary to purify your water effectively.
Do More Filter Stages Equal Better Filtration?
Manufacturers often increase the number of filter stages in their systems, sometimes up to 10! However, this may be unnecessary and more of a marketing tactic than anything else. The number of steps does not solely determine the performance of any type of water filtration system. Factors such as filter design, surface area, water flow rate, and types of filter media used also play a role.
While more stages can potentially improve contaminant reduction, simply repeating the same filter media consecutively may not enhance filtration efficiency. The truth about filter stages lies in finding a balance between incorporating different types of media or methods and increasing the volume of the same media to achieve higher rates of contaminant removal.
Further Reading:
What’s the Minimum Number of Filter Stages Required for RO?
To ensure proper operation, pre-filtration is necessary to protect the reverse osmosis membrane from sediments and chlorine. Both can be removed using activated carbon. A carbon post-filter is usually recommend to give the water a final polish.
So, at a minimum, 3 stages are required for reverse osmosis.
For optimal cost and performance, a recommended setup includes four stages: sediment filtration, carbon filtration, reverse osmosis, and post-filtration for refining, especially with a system that has a storage tank.
Further Things to Consider
Aside from the number of stages in your RO setup, there are a few other things to consider.
Your Water Quality and Needs
When considering feed water quality, various factors come into play.
- For instance, if eliminating bacteria is a concern, a UV filter might be necessary.
- Those with heavy sediment in their feed water could benefit from an additional sediment filtration step.
To assess your specific needs, it’s best to test your water and determine what you want to remove.
Personal preference also plays a role in choosing the stages of your RO system. You may only need to eliminate the residual taste of chlorine, in which case a carbon filter could suffice. On the other hand, if you want guaranteed pure water regardless of contaminants, a 3-stage RO system is a great choice. If you’d like pure water with minerals re-added for taste, a system with a remineralization filter is ideal. Know what you want before you begin shopping.
Installation
The bigger the RO system and the more stages it has, the trickier it may be to install. For example, a simple countertop model is a breeze, possibly requiring no installation at all! A 3-stage under sink system may be a bit trickier, especially if you are short on space.
System Footprint
When it comes to water filtration systems, space is a crucial factor to consider. Compared to a simple carbon filter, multi-stage reverse osmosis systems require more room due to additional filtration steps and the need for a drain line. Similarly, tank systems have more significant space requirements compared to tankless systems.
Maintenance
The number of filtration steps in an RO system usually determines the level of maintenance required (more steps equals more care), but there are exceptions.
Multi-stage systems with multiple filter materials in one cartridge offer easier installation and less frequent maintenance. The lifespan of each filter varies, with the sediment and carbon filters lasting around 6 to 12 months, and the reverse osmosis membrane lasting 2 to 5 years. UV light bulbs need yearly replacement. A remineralization filter often lasts 1 to 2 years.
Your Budget
The more filtration steps you have, the more expensive the system usually is. Not only to purchase but also when considering the filter replacements in the yearly running costs.
If you have any questions about 3 vs 5-stage reverse osmosis please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
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