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What Is an Ion Exchange Water Filter?

Whether you source the water for your home or business from a nearby well or your city’s municipal water supply, you should take every possible precaution to make sure your water is free of harmful contaminants. 

A popular, effective, and safe option for treatment is an ion exchange water filtration system, which can soften water. What exactly is an ion exchange filter, and how does it work?

In this guide, we’ll explore everything you need to know about the ion exchange process, how it’s used in water treatment, and the benefits of using an ion exchange water filter to soften your home’s or business’ water. 

What is Ion Exchange?

Before we get into the nitty-gritty of water softening, let’s take a step back and examine just how ion exchange works to soften water with a quick chemistry refresher:1

  • An atom is made up of three small components—protons, neutrons, and electrons. Protons have a positive charge, electrons have a negative charge, and neutrons don’t have a charge at all.
  • Multiple atoms can link together to form molecules and compounds via electronic bonding. The atoms that make up molecules share electrons, creating a bonded structure.
  • When molecules or atoms lose an electron during the bonding process or gain a proton as the result of a chemical reaction, they develop a positive or negative charge. If a molecule or atom has a positive or negative charge, it becomes an ion.
  • Not all charges are created equal—different atoms and molecules develop charges of different strengths depending on the number of electrons or protons gained or lost during the bonding process or a chemical reaction.

During ion exchange, an atom or molecule will detach its weak bond and reattach to a separate ion with a stronger charge.2 Scientists can use ion exchange to potentially create new molecules and compounds, neutralize electrically-charged atoms, or remove solids from liquid solutions.

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How Do Ion Exchange Water Filters Work?

So, how does an ion exchange system work in water treatment? Ion exchange water filters soften water but don’t filter it. In other words, they use electronically charged solids to remove contaminant ions from drinking water—even if the contaminants are in liquid form. Let’s demystify a few questions about ion exchange in water filtration. 

Which Ions are Exchanged?

There are two types of ion exchange:3

  • In anion exchange, negatively charged ions detach from weak bonds in favor of forming a stronger bond with a different atom or molecule.
  • In cation exchange, positively charged ions detach and reattach in the same fashion as their negative counterparts.

Most ion exchange water filters harness both anion and cation exchange to remove as many contaminants as possible from the drinking water supply. Since not all contaminants are negatively or positively charged, using both methods may ensure thorough water softening. 

Anion exchange may effectively remove the following negatively-charged ion contaminants:4

  • Arsenic
  • Chromium-6
  • Cyanide
  • Nitrate
  • Perchlorate
  • Sulfate
  • Uranium

Cation exchange may remove positively-charged pollutants like:

  • Calcium
  • Magnesium
  • Barium
  • Radium
  • Strontium

Anion exchange typically replaces contaminant ions with chloride, while cation exchange usually relies upon sodium as an exchange ion. Both negatively and positively charged ions are innocuous and may be safe for human consumption in small quantities.

What Does an Ion Exchange Filter Look Like?

While various filters with different designs are available on the market, ion exchange water filters are typically made from a few key components:

  • Inlet and outlet valves for water entrance into and exit from the filter tank
  • Mesh filters to prevent solids from escaping from the filter tank
  • Ion exchange resin

Ion exchange resin typically comes in a solid form, and it’s usually made of small beads. Filter manufacturers use beads (instead of a contiguous substance coating the walls of the tank) for a few reasons:

  • The spherical beads expose more surface area of the resin, increasing its overall bonding capacity.
  • The spherical shape makes it easier for the resin to move throughout the tank when needed to collect as many ions as possible. 

Some systems may also include a resin regeneration tank. When the resin collects its maximum amount of contaminant ions, it moves to a saltwater tank. The contaminant ions attach to the sodium chloride ions in the brine, removing them from the resin, which can then be reused in the primary ion exchange tank. 

In such systems, using spherical resin provides mobility. The spent spheres can easily move into the saltwater tank and back into the primary ion exchange tank once the sodium chloride has removed all contaminant ions.

How Effective Are Ion Exchange Filters?

An Ion exchange water filtration system may be very effective when softening water for two primary reasons:

  1. The chloride and sodium ions used in the resin have very strong electric charges. When they pull contaminant ions from the water supply, the pollutant ions stay attached to the resin very effectively.
  2. Since resin can be refreshed using a brine solution, systems with a built-in brine tank ensure that there’s always resin available to perform ion exchange. This results in efficient and constant chemical reactions. Instead of worrying about changing a filter or adding fresh chemicals, ion exchange water filter users can, essentially, “set it and forget it” without worrying about reduced efficacy over time. 

According to the US Environmental Protection Agency (EPA), both anion and cation exchange can remove up to 99% of negatively- and positively-charged contaminants, respectively.3 Since they’re so effective, the EPA has deemed ion exchange water filters as a “best available technology” and Small System Compliance Technology, particularly for removing radium, uranium, beta particle, gross alpha, and photon emitters.

Benefits of Using an Ion Exchange Filter

While their dependability and effectiveness may make them an excellent choice for home and business water purification needs, ion exchange water filters also offer an array of other potential benefits. Let’s explore a few.


As we’ve discussed above, the resin ion exchange medium is reusable. Ion exchange water filters with built-in saltwater tanks may be the most sustainable option since they don’t require refilling or removing the resin. That also means there’s no need to transport or dispose of exhausted resin. 

Even if a system doesn’t have a built-in brine tank for resin regeneration, home and business owners or their water filtration services providers can replace the resin in their tank and remove the spent beads. Instead of simply throwing away the resin and creating waste, they can refresh the resin for reuse. 

Multi-Chemical Removal

Ion exchange water filters are particularly attractive because of their broad and thorough removal of contaminant chemicals. 

As discussed above, combined anion and cation exchange systems not only remove up to 99% of their target contaminant ions but also remove 12 total distinct pollutants. While some softening systems only target solids of a certain size or a few specific chemicals, ion exchange filters may effectively remove numerous possible contaminants from the water supply. 

Since they have the potential to remove so many different ions, ion exchange water filters may be useful for both pollutant removal and improvement of overall water quality and softness. They may also considerably improve the taste, color, and odor of drinking water  and neutralize tasteless, odorless, and colorless hazards. 

Softening Water Hardness

Water hardness describes the total amount of dissolved magnesium and calcium in your drinking water supply.5

But filtering hard water from your drinking water supply isn’t the only thing that’s important. Since cation exchange water filters remove calcium and magnesium ions from drinking water, they may resolve water hardness issues befalling your home or business. 

Water softening efforts carry multiple potential benefits:

  • Since hard water chemicals neutralize soaps, softer water requires less soap for dishes, handwashing, and bathing.
  • Hard water solids can build up in plumbing systems, potentially causing clogs and pipe cracking. Removing these solids can prolong the life of your plumbing system and ensure optimal water pressure.
  • While magnesium and calcium are essential nutrients for human consumption in small quantities, hard water can provide more of these nutrients than your body needs. Softened water can help you meet your wellness goals.
  • Water softeners reduce difficult-to-remove hard water stains on glasses, plumbing hardware, and surfaces.

You can also learn how to test water quality at home to determine when a water softener may be needed. 

Use in Whole-Home or Whole-Business Systems

Whole-home or whole-business water softening systems are often the simplest solutions for improving drinking water quality. 

Other water softening solutions are available, of course, but they all carry their own drawbacks:

  • Countertop filter pitchers use filtration media that degrade with time, and they don’t always target multiple contaminants. Users must remember to replace the filters—a process that costs money and creates waste.
  • Sink-only systems can be useful for some drinking water needs, but for homes and businesses with hard water issues, sink-only systems only prevent hard water damage in one specific area. 
  • Freestanding or refrigerator water filters also incur lifetime costs, and they don’t resolve hard water issues that can cause long-term plumbing system damage. 

Since ion exchange water filters can be used in a whole-home or whole-business softening system, you can reap the potential benefits of their effective treatment throughout your entire space. 

Add an Ion Exchange Filter with Rayne Water 

Ion exchange water filters may be effective and sustainable—and may also target a wide variety of potential water supply contaminants to soften water. If you’re in search of a water softening solution for your home or business, you should certainly consider an ion exchange solution for your drinking water needs. 

Making a shortlist of potential business or house water filter systems can be difficult without professional advice. At Rayne Water, we bring almost a century of experience to home and business owners. We’re passionate about bringing you the cleanest, tastiest water possible, and we’re ready to help you, your family, or your business find the ideal solution. We have locations in Arizona, California, and Nevada. So if you need a water softener in Sacramento or a reverse osmosis system in Phoenix… we’ve got you covered!

When you’re ready to improve your water quality, contact us for a free consultation. 

Find a location near you!


  1. Northwestern University. What Is an Ion? 
  2. ScienceDirect. Ion Exchange. 
  3. US Environmental Protection Agency. Radionuclides in Drinking Water.
  4. US Environmental Protection Agency. Overview of Drinking Water Treatment Technologies. 
  5. US Department of the Interior. Hardness of Water.