5-Stage vs 6-Stage Reverse Osmosis Systems

This page may contain affiliate links. If you buy a product or service through such a link we earn a commission at no extra cost to you. Learn more.

When comparing water filtration systems, reverse osmosis systems usually come with 5 filter stages.

What sets a 6-stage system apart is the inclusion of a unique filter stage, often dedicated to remineralization or UV treatment (or both).

So, is a 6th and potentially more expensive stage needed? Let’s see.

Key Takeaways

  • 5-stage reverse osmosis systems contain five filtration steps but can vary in configuration. Often, there are sediment and carbon prefilters, the RO membrane, a carbon post filter, and possibly remineralization.
  • 6-stage reverse osmosis systems are pretty similar in their configuration to 5-stage RO systems, but a 6-stage is likely to have an extra ‘special’ type of filter. This could be a UV filter or a remineralization filter.
  • Which setup to choose should be based on your water quality and personal preferences.

Difference Between 5-Stage and 6-Stage RO Systems

First of all, what’s the difference between a 5-stage versus a 6-stage reverse osmosis system?

Well, 6-stage reverse osmosis systems are pretty similar in their configuration to 5-stage RO systems, but a 6-stage is likely to have an extra ‘special’ type of filter. This could be a UV filter or a remineralization filter.

5-Stage Reverse Osmosis Systems

Several combinations of filter stages are available in a 5-stage RO system for water purification. These include the following setups:

  1. Three pre-filters consisting of two sediment filters and one carbon filter, followed by an RO membrane and a carbon post-filter.
  2. Three pre-filters consisting of one sediment filter and two carbon filters, followed by an RO membrane and a carbon post-filter.
  3. Two pre-filters consisting of one sediment filter and one carbon filter, followed by an RO membrane, a carbon post-filter, and a remineralization filter.
  4. Two pre-filters consisting of one sediment filter and one carbon filter, followed by an RO membrane, a carbon post-filter, and a UV lamp.

Under Sink Reverse Osmosis System

To illustrate, a typical setup would involve the following stages:

  1. Sediment prefilter: It effectively removes larger dirt and debris particles protecting the RO membrane from clogging.
  2. Carbon prefilter: This filter helps reduce elements like chlorine and other contaminants/impurities that can cause unpleasant tastes and odors in the water. Chlorine can also damage the reverse osmosis membrane so it’s important to remove beforehand.
  3. 2nd carbon prefilter: Further reduction of elements causing unpleasant taste and odor, including chlorine.
  4. RO membrane: The membrane does the bulk of the contaminant removal: Salts, heavy metals, microorganisms, microplastic, asbestos, and other chemicals and compounds.
  5. Polishing filter: Removes residual taste/odor.

6-Stage Reverse Osmosis Systems

6-stage reverse osmosis systems are comparable 5-stage setups in terms of the various filter types that can be utilized. There are numerous setup possibilities.

  • For instance, one option is to incorporate three pre-filters consisting of two sediment filters and one carbon filter, along with the reverse osmosis membrane and a carbon post-filter paired with a remineralizer.

Alternatively, a combination of one sediment filter and one carbon pre-filter, along with the RO membrane, a carbon post-filter, a remineralization filter, and a UV filter can be employed. The choice of setup depends on individual requirements and preferences.

How Do the Different Filter Stages in a Reverse Osmosis System Work?

All the stages within a reverse osmosis system are designed for specific contaminants and work synergistically together.

Sediment Pre-Filter

Sediment filtration is a critical step in water purification, as it effectively eliminates debris from the water. Positioned at the start of the filtration process, it captures larger particles, enabling the subsequent stages to target other contaminants without getting clogged.

Carbon Pre-Filter

During the carbon filtration stage, water passes through activated carbon in granular or block form, eliminating tastes, odors, cloudiness, colors, and all kinds of chemicals.

As a result, any residual chlorine taste, often present in municipal water, is eliminated.

Reverse Osmosis Membrane

During this critical phase, water passes through a semipermeable membrane with ultra-small pores measuring 0.0001 microns. A remarkable 99% of impurities, including the particularly nasty ones like lead and nitrates, are eliminated from the water.

Carbon Post-Filter

After undergoing reverse osmosis, water is often perc sitting in a storage tank. Incorporating a coconut shell carbon post-filter eliminates any lingering taste once the water leaves said tank.

UV Light

An ultraviolet (UV) purifier is an optional component that can be added to a 6-step RO system. It proves beneficial when the feed water contains microorganisms, such as bacteria or cysts. This purification stage utilizes ultraviolet light to kill pathogens in the water, preventing their reproduction.


A remineralization filter is an additional filtration stage that can be added, replenishing the water with essential minerals such as calcium and magnesium for taste and health. This imparts a subtly mineralized flavor to the water, along with an increase in pH level.

5-Stage vs 6-Stage Reverse Osmosis Systems – Which to Choose?

So which is better, a 5-stage or a 6-stage reverse osmosis system?

Well, it depends. Not every 5 stage and 6-stage reverse osmosis setup is the same. So the question really is, what filter stages are being used?

If your water is contaminated with microorganisms, plus you prefer remineralizing your RO water before consumption, then the right 5-stage or 6-stage RO system can both work.

Is More Filter Stages Better?

Manufacturers often add extra filter stages to their systems for no reason except marketing and upselling. The number of steps alone doesn’t determine filtration system performance. While more stages can potentially improve contaminant reduction, repeating the same filter media consecutively may not enhance filtration efficiency. You have to look at the contaminants in your water and then determine if you need an extra step or two in your system.

What Else to Consider

Some things to consider when determining how many stages in your RO system and what configuration include:

Water Quality

Assess specific needs by testing water and determining the necessary stages, such as employing UV filters for bacteria elimination or adding sediment filtration for heavy sediment.

Your Preferences

If you just want to get rid of the taste of chlorine, a carbon filter might be enough. To have pure water with minerals added back for taste, consider a system with a remineralization filter.

Make sure to clearly understand what you want before starting your shopping journey so you aren’t unnecessarily upsold.

Installation and Maintenance

under sink reverse osmosis system

Installing a larger system with multiple stages can become increasingly challenging. While a 3-stage system can be easily installed at home, a 10-stage system may pose difficulties, mainly if space is limited.

The maintenance level of an RO system usually depends on the number of filtration steps, although there are exceptions. Multi-stage systems with multiple filter materials in one cartridge are easier to install and require less frequent maintenance. Typically, the system becomes pricier with each additional filtration step. This applies not only to the initial purchase but also to the annual running costs when accounting for filter replacements.

If you have any questions about 5 vs 6-stage reverse osmosis please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
Learn more about .


Information provided on BOS is for educational purposes only. The products and services we review may not be right for your individual circumstances.
We adhere to strict editorial guidelines. Rest assured, the opinions expressed have not been provided, reviewed, or otherwise endorsed by our partners – they are unbiased, independent, and the author’s alone. Our licensed experts fact-check all content for accuracy. It is accurate as of the date posted and to the best of our knowledge.

Leave a Comment: