There are two broad categories of water softening systems used to treat hard water: salt-free systems and ion-exchange systems which require the use of salt. Understanding how a salt versus salt-free water softener systems work and the advantages or disadvantages of both can be beneficial if you are exploring water softening options.
Before diving into how does salt soften water, it is useful to gain a good understanding of how water becomes hard in the first place. Understanding this process can help you gain a better sense of how salt is used to soften water.
Water becomes hard naturally over time as it passes through soil and stone rich in minerals. The most common minerals in hard water are calcium and magnesium, usually in the form of bicarbonates, sulfates, and chlorides. Metals like iron, lead, and aluminum can also cause water to become hard.
As water percolates through ground rich in minerals it dissolves the bonds between some mineral ions, attracting these ions to the water molecule itself. These hard water minerals remain bonded to the water molecules until they are deposited as an insoluble precipitate on surfaces the water comes in contact with. These deposits are known as scale.
Water is described as “hard” when it has a high content of minerals. Alternatively, water is considered “soft” if it has a very low content of dissolved minerals. The exact hardness of your water is determined through a test that measures the number of grains-per-gallon (GPG) of calcium carbonate a sample of water contains. Once this number is determined it is compared to the water hardness scale.
The water hardness scale is as follows:
In weighing a salt versus salt free water softener (which is actually defined as a water conditioner) it is helpful to start by understanding how systems using salt work since they are an older and more common method. Water softening systems use salt to soften water through a process known as ion-exchange.
Ion-exchange systems function by removing mineral ions from hard water and replacing them with sodium ions. Here are a few important things about this process to understand from the outset:
A standard ion-exchange system will have two tanks. The first tank contains negatively charged resin beads and is often referred to as the resin tank. The resin beads in the tank are coated with sodium ions. The second tank contains a salty brine solution and is known as the brine tank.
When hard water enters the system it passes through the resin tank. As it moves through the tank the mineral ions in the hard water, which are positively charged, are attracted away from the water molecule and towards the negatively charged resin. The mineral ion is exchanged with the sodium ions, allowing the water molecules to pass through the system to maintain a balanced charge.
Ion-exchange water softeners are often installed where the municipal water line enters your home. This allows water softeners to provide soft water to your entire home, which is important if you want to eliminate the problems associated with hard water. These systems will require access to an electrical outlet, and they will also need a drain.
Ion-exchange systems require a drain because periodically the minerals removed by the system will need to be flushed. The flushing process is fairly straightforward; salty water from the brine tank is used to fill the resin tank. The high salt content in the water replaces the minerals that have been collected on the resin with sodium ions. The remaining brine solution which now contains the minerals captured by the system is then flushed down the drain. Occasionally, the owner will have to add salt for a water softener to the brine tank for the next regeneration cycle.
Some people are apprehensive about ion-exchange systems because of the sodium content in the soft water they produce. While the softened water does contain sodium, it only contains a small amount. The actual sodium content of the water will depend on how hard your water was when it entered your system. Harder water will require more sodium to soften.
The sodium content of softened water is very low and can’t be tasted. If you have health concerns, you can consider installing a point-of-use (POU) reverse osmosis system at your sink to provide drinking water. Reverse osmosis systems can function as a salt water filter, leaving you with softened and filtered water.
Water softeners that don’t use salt offer an alternative to ion-exchange systems, but function in a fundamentally different way. First one must understand that a salt-free water softener is actually a water conditioner — as this is commonly mistaken.
One way to remove the mineral content from hard water is through physical filtration. The more common salt-free method to soften water is to use a water conditioner. A salt-free water conditioner leaves the minerals in hard water but eliminates the negative impact they have around your home. Let’s take a look at each of these in greater detail to decide the best salt free water softener for you.
Physical filtration of hard water minerals is probably the least common of the three types of water softening systems, but it is worthwhile to understand because it can be a viable option. Physical filtration is the process of passing water with unwanted contaminants through a membrane containing pores small enough to allow water molecules through but not small enough to allow minerals and metals through.
Reverse osmosis systems are the most common way to filter the mineral content of hard water. Reverse osmosis systems function by forcing water at pressure through a membrane containing very small pores. Water molecules are able to pass through the pores, while the minerals and metals in hard water aren’t allowed to pass. Sodium chloride is also filtered by reverse osmosis systems, making them effective salt water filtration systems.
While highly effective at reducing minerals and other contaminants in water, reverse osmosis systems tend to be used to provide drinking water at a single tap rather than filter all of the water coming into a home. However, whole-house reverse osmosis systems are an option. The advantage of these systems is: they not only soften water by removing minerals and metals but also remove other contaminants like microbes.
Rather than softening water, salt-free systems condition the water. Water conditioning treats the water so it doesn’t cause scaling. Hard water deposits minerals like calcium and magnesium as scale, an insoluble precipitate that builds up on surfaces, fixtures, and appliances around the home.
At the core of these systems is template-assisted crystallization (TAC) media. As water passes over this special material, the calcium and magnesium bicarbonates in hard water are precipitated out of the water as small crystals, sometimes referred to as “seed-crystals”, before they can form into scale.
Normally, when hard water passes through pipes or flows over surfaces and fixtures the minerals in the water deposit on those surfaces. With conditioned water, the seed crystals created as the water passed over the TAC media are a more attractive deposit point than the surfaces the water is passing over or through.
So, with a water conditioner, the seed-crystals in the water collect the minerals before scale can form. These systems don’t actually remove the mineral content from hard water, but instead change the minerals to eliminate their harmful impact. This is distinct from ion-exchange systems that remove minerals from hard water and replace them with sodium ions.
Water conditioners can still be used to help avoid the harmful impacts of hard water. These systems are capable of providing conditioned water throughout your entire house. Additionally, water conditioners don’t require electricity, unlike ion-exchange systems. This makes them great for installation in areas of your home without ready access to an electrical outlet.
Water conditioners are also a great way to enjoy the benefits of soft water in areas with brine restrictions. Some cities restrict the disposal of brine wastewater, which is a key component of ion-exchange systems.
If you are exploring your options for producing soft water throughout your home, you’ll come across systems using salt and systems marketed as salt-free. These systems function in distinct ways. Ion-exchange systems use salt because they exchange the mineral ions in hard water with sodium ions.
In contrast, salt-free systems condition hard water to reduce its impact. This conditioning process involves changing the minerals contained in hard water into a crystalline structure before they can form a scale. While water conditioners don’t remove the minerals from hard water, they do ensure the harmful impacts of hard water are avoided. It is also possible to use a reverse-osmosis system to physically filter the mineral content from hard water, though this is less common as a whole-house solution.
These two different types of systems have advantages, and understanding these advantages can help guide you towards the right water softening solution for you. Water conditioners are advantageous if you live in an area with brine restrictions, or when access to electricity or a drain near the installation point is unavailable.
To learn more about the advantages of these different water softening solutions, please contact Rayne Water today. Our water quality experts will be able to walk you through the available systems and provide you with a comprehensive breakdown of each. Additionally, see our guide to water softener alternatives you may not be aware of.