Water softeners are used around the world to remove dissolved minerals from household water supplies. Installed between the municipal water supply piping and the household plumbing fixtures, water softeners rely on principles of chemistry – particularly the phenomenon of ion exchange – to purify and soften water used for drinking, cleaning, and bathing. Inside the water softener system lives a specially formulated material known as “softener resin”, sometimes called “cation resin”. In this guide, we will dive deep into resins, including what they are, what they are made of, how they work to purify clean, freshwater.
Water Softeners: The Basics
Most of the households in the United States are supplied with “hard” water, or water that has high levels of dissolved minerals like magnesium, calcium, and trace elements. Water softeners are designed to remove those dissolved minerals from water supplies. The typical whole-home water softener system is comprised of two tanks: a tall water softener tank filled with resin beads, and a smaller brine tank containing water mixed with potassium chloride or salt. Tubing connects the two tanks. Some systems include pre-filters to screen out silt and debris from water supplies before it enters the softener tank. Many water softener system tanks contain loose resin beads, while others are equipped with resin cartridges for easy replacement.
The Magic of Ion Exchange
Now that we have a basic understanding of water softener systems, how do they work? These systems rely on a chemical process known as ion exchange. Polymeric ion exchange resins – the resin beads inside the water softener tank – are negatively charged. The dissolved minerals in water supplies have a positive electric charge. The resin beads attract molecules of dissolved minerals and bind to them in the ion exchange process. Once the water passes through the resin, it continues to the plumbing fixtures like sink faucets, ice makers, and washing machines. The minerals have been removed and the water’s clarity, taste, and odor are improved. Water softener resins bind to:
- Organic compounds like carboxylic acid
What is Water Softener Resin?
Ion exchange is made possible by water softener resins. Many people with water softener systems have many questions about these resins, including:
- What is water softener resin made from?
- What is in water softener resin?
- What is the color of ion resins in water softeners?
- What media resin is best for hard water?
- What resin should I use for water softeners?
The answers to these questions depend on what the resin is made from. Typically, cation resins are made from a food-safe insoluble material called crosslinked polystyrene divinylbenzene or polystyrene sulfonate. Approved by the U.S. Food and Drug Administration (FDA) for use in the treatment of water and foods for human consumption, the resin beads range in size from 0.3mm to 1.2mm, with most of the individual beads measuring under a millimeter in diameter. The beads vary in color from whitish to light tan, to amber, brownish-yellow or dark brown.
Cation resins are porous, allowing for greater surface area to trap the dissolved mineral ions. In addition, to use in whole-home water softener systems and travel water softeners, ion exchange resins are also used in purification and decontamination processes in the pharmaceutical, agricultural, and manufacturing industries.
How Much Resin Goes in a Water Softener?
The amount of cation resin used in water softeners varies by size and model. Water softener systems are often rated by “grain capacity”. Smaller portable water softeners rated for 16,000-grain capacity typically use about ½ cubic foot of resin media, while larger models rated at 32,000-grain capacity will use a full cubic foot of the ion exchange resin. How often should water softener resin be replaced? The replacement schedule for ion resins also varies by the size of the system, the manufacturer’s recommendation, and the amount of water being treated by the system. Under normal use, the resin in a water softener system may last for years, provided regular regeneration (see below) is performed. In certain areas, such as cities with high levels of dissolved iron or chlorine in the water supply, the resin may need to be replaced more frequently.
If you are wondering how to empty a water softener resin tank, many manufacturers offer easy disconnects to dump out the tank and pour new cation resin in with a funnel. Other systems are equipped with screw-in or drop-in resin cartridges for effortless replacement. Once the old resin has been removed from the system, it can be discarded with household trash. Check with your local waste disposal company for specific regulations or guidance in discarding used ion resins.
Can Ion Resin Be Regenerated?
Over time, the resin in a water softener tank will lose its ability to exchange ions with dissolved minerals like calcium and magnesium. This reduces the effectiveness of the softener. The resin media can be regenerated, however, and the process is where the smaller brine tank comes into play.
When the softener resin beads are ready to be regenerated, salty water from the brine tank is piped into the softener tank. By flooding the resin with the very ions it attracts – the positively-charged salts in the brine mixture -- in the exchange process, it causes the excess minerals to drop out of solution, thus refreshing the porous surface area of the beads. The regen water is drained out of the softener tank through a special valve, and the resin is once again ready to perform its softening process.
In larger whole-house water softener systems, the regen process is automatic; a computer controls the timing and duration of the regeneration. Smaller travel water softeners, such as those in RV water softener systems, may need manual regeneration based on average water use or its water treatment rating. Regardless of the system, regeneration typically takes about 90 minutes to complete.
Where Can I Buy Water Softener Resin?
When it is time to replace your water softener resin, finding replacement resin media is as easy as visiting an online water softener company and placing an order. Softener resin is available in cartridge and loose formats. The loose bagged media is typically sold in ½ and one cubic foot quantities, which match the capacities of a wide number of systems on the market. Ion resins are rated by quality, particle size, and operating parameters; experts in water softener systems can help you determine which is the best media replacement for your own system.