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How Does a Water Softener Work?

If you are considering transitioning to soft water throughout your house, you are probably wondering “how does a water softener system work?”. Water softening systems are an effective method of producing soft water for your entire house, but most people aren’t clear on the various types of water softeners, as well as how they function exactly.

Water softening systems transform hard water into softened water through a process known as “ion exchange”. Ion exchange is a gentle, yet highly effective method of removing the mineral ions that lend to the level of hardness found in some water. To understand how these systems function, you’ll first have to understand exactly what soft water is, and how water becomes hard in the first place. By gaining a full understanding of this process, you’ll have a better grasp of how water softening systems function and whether installing a water softener is the right choice for you and your home.

What is Water Hardness?

Don’t know the difference between hard water vs. soft water? Water is often referred to as either “soft” or “hard”, but the meaning of these terms isn’t intuitive. Both of these terms are tied to the concept of water hardness, which is used to communicate the mineral content of a sample of water. Regardless, the benefits of soft water most definitely differentiate it from hard water.

Water hardness exists on a spectrum, from “soft” water which has a very low concentration of hard water minerals, to “very hard” water which can have a relatively high concentration of hard water minerals. This spectrum is better understood by looking at the water hardness scale. The water hardness scale is used to quantify exactly how hard or soft a sample of your water supply is. The most common scale in use measures the mineral content of water in terms of the number of grains-per-gallon (GPG) of dissolved calcium carbonate that a sample of water contains. Grain capacity can be broken down into several tiers based on calcium content.

Here are the thresholds for water hardness as defined by the most commonly used water hardness scale:

  • Water containing less than 1 GPG of calcium carbonate is considered soft.
  • Water containing between 1-7 GPG of calcium carbonate is considered moderately hard.
  • Water containing between 7-10 GPG of calcium carbonate is considered hard.
  • Water containing over 10 GPG of calcium carbonate is considered very hard.

What is notable about the water hardness scale is that water can exist with varying degrees of hardness. It is also important to understand that the water hardness scale measures the amount of calcium carbonate that a sample of water contains because it is the most common mineral contained in hard water, but water hardness can be affected by many types of minerals and metals. Other common dissolved minerals found in hard water include magnesium, iron, manganese, zinc, aluminum, barium, and others.

How Does Water Become Hard?

The process through which water hardens is important to understand because it directly informs an understanding of how these systems work to soften water. Starting at the beginning of the water cycle, precipitation falls to the surface of the Earth as soft water or water with relatively low mineral content. Water begins to harden as it flows over and seeps through mineral-rich ground and soil.

Surface water, or water flowing through rivers and streams, tend to have a lower content of hard minerals. Groundwater tends to have a much higher content of hard minerals, as it moves through soil and stone rich in minerals. This groundwater eventually ends up in the aquifers that supply water to our homes.

As water percolates through soil and stone it picks up positively charged mineral ions. These ions become bound to the water molecule and typically aren’t separated from the water molecule until the water evaporates and leaves the mineral ions behind as deposits. As we will see, this process is important for understanding a water softener system and how does it work.

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How Water Softening Systems Work

If you have ever wondered, “how does a water softener work?”, the answer is that water softening systems remove mineral ions in hard water through the process of ion exchange. This process requires exchanging positively charged mineral ions in the hard water with positively charged sodium ions, leaving the water coming out of the system free of mineral ions.

Water softening systems contain two tanks: a brine tank and a resin tank. Let’s break down the function of each of these.

Resin Tank

When water enters the water softening system it enters the resin tank. This tank holds a fairly sizable amount of plastic resin, usually a few cubic feet. This resin is porous and is usually covered in positively charged sodium ions.

As hard water moves through the resin tank the mineral ions that are bound to the water molecule are attracted to the negatively charged resin. The positively charged sodium ions that coat the resin are released into the water as the mineral ions take their place on the resin. This allows the resin to maintain a balanced electrical charge.

The water exiting the system contains a small number of sodium ions as the result of the process, but importantly no longer contains high levels of hard mineral ions. This process of ion exchange is a highly effective, yet gentle method of achieving softened water. To get a sense of how effective it is, each foot of resin in the system can soften approximately 3,200 gallons of water before it needs to be recharged. Now that would require an ample amount of water usage to go through that many gallons in a short period of time.

Brine Tank

The resin contained in the resin tank of a water softening system needs to be recharged periodically in order to continue removing dissolved minerals from hard water. As minerals are removed from hard water they bind, through an electrical charge, to the negatively charged resin. These mineral ions take up space on the resin, and periodically need to be flushed from the resin to allow other mineral ions to occupy that space. If not done periodically, the flow rate may be impacted.

The second tank in a water softening system is known as a brine solution tank and contains a concentrated solution of saltwater. During the flushing process, the resin tank is rinsed with the saltwater from the brine tank. The saltwater saturates the resin, forcing the positively-charged mineral ions to become removed and replaced by positively charged sodium ions. The remaining water in the resin tank, containing the loose mineral ions, is then flushed and the system is ready to soften water again.

Do Water Softening Systems Require Maintenance?

Water softening systems do require some maintenance to function at peak performance. Specifically, the user is usually required to add additional salt, or sodium chloride, to the brine solution tank periodically.

The process of flushing the resin tank may be automated depending on the specific system you are using. Many systems perform the flushing process in the middle of the night when the system is less likely to be in use.

What About Salt?

Sodium ions serve an important function in water softening systems, but many people are curious about whether the soft water produced by a water softening system is salty. A typical water softening system will add roughly 750 milligrams of sodium for each gallon of water produced. To put this number in perspective, an 8-ounce glass of tomato juice has approximately 875 milligrams of sodium.

With that being said, if you are concerned about the sodium content of soft water there are a couple of treatment options for you. 

First, some types of water softeners utilize a resin that releases potassium into the water rather than sodium. The downside of these types of systems is that the potassium chloride salt used in them is more expensive than the salt used to refresh a typical water softening system.

Second, many people choose to install a reverse osmosis system under their sink to provide water for drinking and cooking. Reverse osmosis (RO) systems are small, making them easy to install in tight places, and they can remove any remaining sodium in the water along with other dissolved solids that your water may contain. It is basically a water conditioning system made to provide fresh drinking water.

Closing Thoughts

Water softening systems are a highly effective and efficient method of removing hard minerals from hard water that could be affecting your health and house appliances. Water softening systems utilize a process known as ion exchange to remove minerals from hard water. This process reverses the natural processes through which water becomes hard in the first place.

When water percolates through soil and stone it picks up positively charged mineral ions, which are then bound to the water molecule and make it hard. Hard water enters the water softening system through the resin tank, which is a tank filled with a negatively charged porous plastic resin coated in positively charged sodium ions. As the hard water moves through this tank, the hard mineral ions in the hard water are attracted to the negatively charged resin. The water exiting the system has had the hard minerals removed, and is ready to be piped throughout your house.

Water softening systems remove hard minerals through a gentle, largely passive process. Periodically the resin’s negative charge needs to be refreshed by removing the mineral ions that have become attached to it during the water softening process. This is accomplished by filling the resin tank with a saltwater brine, which displaces the mineral ions with sodium ions. Those mineral ions are then flushed from the system and the water softening system is ready to soften more water.

Water softening systems are low-maintenance and are the most efficient method of removing hard minerals – calcium chloride, magnesium, iron – from hard water and avoiding the negative impact of hard water throughout your house. Rayne Water is proud to serve California and Arizona. So if you need a water softener in Phoenix or a reverse osmosis system in San Diego… we’ve got you covered! To learn more about what water softening systems are available for your residence or business or how to get a purified water system, please contact Rayne today.



  1. Ungvarsky, Janine. 2018. “Hard Water.” Salem Press Encyclopedia of Science.