There are a number of types of devices that claim to soften hard water, including standard salt-based ion-exchange softeners, salt-less chelation-based water conditioners, and electromagnetic de-scalers.
Watch the video below to understand how does a water softener work.
Salt-Based Ion-Exchange Water Softeners
Salt-based ion-exchange water softeners are the truest form of water softener; they remove hardness-causing calcium and magnesium ions from hard water to ‘soften’ it, replacing them with non-hardening sodium ions from the salt (sodium chloride) contained in their brine tanks.
Calcium and magnesium ions found in water that has passed through limestone or dolomite rock formations before being drawn into the water supply, are the culprits in water hardening. When the water is heated, these ions react with free carbon dioxide and oxygen in the water, to form calcium carbonate and magnesium hydroxide crystals.
These crystals tend to form on hard surfaces in the water system, such as pipes, heating elements and shower heads. As more crystals form and adhere to the existing ones, a hard crust, called lime-scale, builds up and affects the performance of the water system.
Results are less water flow through pipes, less heating power from electrical heating elements, poorer water pressure at faucets and shower heads, as well as streaking and spotting of glass surfaces, and poor lathering of soaps and shampoos.
In order to prevent the formation and build-up of these lime-scale crystals, salt-based water softeners remove the calcium and magnesium ions from the water by replacing them with sodium ions in a process called ion-exchange.
These water softeners contain two tanks, although one might be enclosed in the other, or they might both be enclosed in a single unit, to appear as a single tank. One tank is called the brine tank, and it needs to be topped up with salt on a regular basis, the other tank is called the resin tank, it contains the resin beads that are used in the ion-exchange process.
The resin beads are 1mm to 2mm (1/25” to 1/12”) in diameter and are key to the process. They contain a layer of sodium ions which replace the hardness-causing calcium and magnesium ions when hard water is passed through the column of resin beads, in order to produce softened water. As more hard water is softened through this process, fewer sodium ions remain on the resin beads, until they cannot effectively soften any more water.
At this stage, the system needs to be ‘regenerated’ – that is, the calcium and magnesium ions that have been captured by the resin beads need to be removed and replaced by further sodium ions. This is achieved by mixing more salt-laden water (brine) from the brine tank with the resin beads in the resin tank. The strength of the salt (sodium-chloride) in the brine solution causes sodium ions to displace the calcium and magnesium ions from the resin beads, and the hardness ions are rinsed away with waste water.
In order to sustain the water softening process over the 10 to 15-year lifespan of the resin, the resin needs to be ‘regenerated’ about every 7 days, and it is also necessary to add more salt to the brine tank regularly, about 25 lbs (11kg) every month or so. Care must be taken to use solar salt or salt pellets, but not mineral salt, as the latter may contain impurities which will negatively affect the performance of the water softener.
People on low sodium diets who are concerned about additional sodium in their drinking water can substitute potassium chloride for the sodium chloride salt used in the brine tank, this will work just as well, but is a somewhat more expensive compound.
Salt-Free Water Softeners
These devices do not use a salt-based (or potassium-based) ion-exchange process to reduce scale formation in water. They are correctly termed water ‘conditioners’ or ‘de-scalers’ rather than water softeners, and use what is known as ‘physical water treatment’ (PWT) methods to sequester hardness ions, preventing them from reacting with other chemicals in the water to form lime-scale.
Some systems use a process of ‘chelation’ to form a complex between the ions of hardness-causing minerals and the molecules of the chelating agent. This process deactivates the hardness ions, so they remain in suspension in the water and are unable to form hard scale when heated. The basis for many chelating agents is food-grade citric acid, a source of vitamin C.
Another salt-free water conditioning process is known as Template-Assisted Crystallization (TAC) or Nucleation-Assisted Crystallization (NAC). In this process, beads similar to the resin beads in ion-exchange processing are used, but they are coated with ‘catalytically active sites’ or templates which attract hardness ions (calcium, magnesium) and their counter-ions (bicarbonates), allowing them to combine and form inert ‘seed crystals’.
When a large enough number of these inert crystals have coalesced, the crystal cluster breaks away from the resin bead and flows through the water system, unable to attach onto any surfaces in the form of lime-scale.
Where ‘conditioned’ water evaporates, it will leave a thin white layer of powdery crystals that can easily be wiped away, unlike lime-scale that is difficult to remove.
TAC devices are available in the form of tanks containing beads or filter cartridges with the TAC media embedded, and the inert crystals will last for up to two days, so the TAC system is not suited to circulating water systems, but is very effective where water flowing through the system is consumed or disposed of in a fairly regular manner. The same is true for chelation-type water conditioners, but these are mainly available in the form of replaceable cartridges.
The advantages of these two types of water softener/conditioner are that they do not use salt, need no electricity and have very low maintenance requirements compared with salt-based ion-exchange water softeners.
Cartridges last in the order of six months each and can quickly and easily be changed. Many users have reported that these systems also improve lathering of soaps and shampoos in the conditioned water as well.
A third type of water ‘softener’, technically classed as a de-scaler, works on the principle of electromagnetic pulses that alter the state of metal ions in the water, including calcium and magnesium, so that they do not react with other chemicals in the water when heated to form lime-scale.
Electromagnetic de-scalers have been scientifically tested and, although they did not perform as effectively as the other types of water softeners discussed here, they were shown to prevent at least 50% and up to 88% of scale formation from hard water.
The exact mechanism of electromagnetic de-scaling has not been settled on, however, the use of electromagnetic pulses has been found to be more effective than the use of permanent magnets, as they simulate multiple passes of the water through a magnetic field.
Electromagnetic de-scalers require no maintenance, only a small amount of electricity, and have been found to reduce existing lime-scale over time.
These devices consist of a small control box with a mains plug and two very low-voltage wires which are wrapped around the water pipe a specified number of times. That’s it, plug in, switch on, and leave it to do its work!
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