One of the more common questions we receive is about the options for drinking water filtration.

Two of the leading technologies for drinking water filtration are carbon-based filters and reverse osmosis filtration.

They are decidedly different technologies with very different levels of drinking water quality.

What is Removed:  Reverse Osmosis v. Carbon Filtration

Water May Contain:“Reverse Osmosis / Carbon Combination”“Carbon Block or Activated Carbon”
Bad/Foul TasteRemovesImproves
Organic Compounds*RemovesRemoves
Chlorine & THMsRemovesRemoves
BacteriaRemovesMay Control Growth**
VirusesRemovesWill Not Remove
CystsRemovesRemoves Some
ParasitesRemovesRemoves Some
ArsenicRemovesWill Not Remove
Heavy Metals***RemovesRemoves Some
Dissolved Solids****RemovesWill Not Remove
FluorideRemovesWill Not Remove

*Organic Compounds – include Pesticides, Herbicides, and Insecticides.

**Silver-Impregnated Carbon – can control bacterial growth.

***Heavy Metals – include Iron, Lead, Cadmium, and Aluminum.

****Dissolved Solids – include Sodium, Calcium, Magnesium, and inorganic minerals.


Carbon Filters

Carbon filtration is one of the oldest technologies on the planet.  These types of filters cover a broad spectrum of options.

On the extreme low-end, that’s carbon gravel.  These are the refrigerator filters or Brita cartridges.  It’s the same carbon gravel you buy in an aquarium store.  These filters will remove some chlorine.

Better filters would be carbon in a block form, some being “activated carbon” or similar.   Most of these will remove more chlorine.

A high-quality carbon filter is often more effective than a low-end reverse osmosis system.  An example of this would be our Always Fresh filter.  It removes 99.99% of chlorine.   It will remove volatile organic compounds and heavy metals.

A reverse osmosis system will use a high-quality carbon filter.  These are often called the “taste and odor” filter.

Reverse Osmosis

Reverse osmosis is a membrane technology.   These thin-film composite (TFC) membranes force water over a semi-permeable membrane.

Most will consist of three stages:

Pre-Filter:  The purpose is to remove sediment and particulate that can ruin the filter.

Membrane: This is the important part and quality matters.  The membrane is what separates out the water from the non-water.

Post-Filter:  This is the taste & odor part of the system.  Carbon filters will “polish” the taste and flavor of the water.

Be wary of 4-stage, 5-stage, or 20-stage systems.  They’re usually just unnecessary, redundant filters.  Read: Gimmick that increases your cost of operation.

Better systems, such as our Kinetico K5 Reverse Osmosis, will have expansion ports.  This isn’t for two taste and odor filters, but for an optional system expansion.  Examples would be specific-purpose cartridges such as:

  • Arsenic elimination
  • Mineral addition / pH adjustment
  • Virus guards

The Difference

These two technologies are different.  Carbon is not bad, we use it for whole-home dechlorination.  When it comes to drinking water, there is a massive difference.

The difference between reverse osmosis and carbon filtration is, simply, that size matters.

Everything in water has a size.  This is measured in microns.  Most carbon filters have NSF Class I ratings.  This means that they remove 85% of particles sized 0.5-1 micron.

Reverse osmosis systems can filter down to .001 micron.  That’s a 500x’s size difference in capacity.

Here is a quick table on items, their size, and why you use reverse osmosis for better drinking water:


  1. doug Bouman

    you don’t mention the amount of water needed to run through a RO system to get a gallon of purified water. It takes many gallons of water to get one gallon of pure water.

    • Chris Richter

      Hi Doug, Thanks for your note. That’s true, it wasn’t referenced. You’re normally looking at 1-1.5 gallons of effluent discharged to make that 1 gallon of clean water. That’s the ‘recovery ratio’ for a system. The many gallons thing hasn’t been true in decades for anything other than the lowest grade of equipment.

      At the same time, that really low grade equipment isn’t going to support the water quality that was the purpose of RO in the first place. That percentage of stuff removed is the ‘rejection rate.’

      So if I have a system that is recovering near 50% (1:1 gallons) and rejecting at 95%+, there is absolutely a gallon ‘wasted.’ That could also be phrased another way though. If I concentrate all the chemicals from two gallons into one gallon, I now have one gallon that I actually want to drink and one that I would prefer not to.

      To each their own & thanks for your comment.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>