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Water softening in its strictest form implies the removal from the water of the minerals that cause water hardness, namely calcium and magnesium – and to a much lesser extent, iron.
So, what are some good methods for softening water? Let’s dive in and see how we can learn how to soften hard water.
The most effective means of achieving this is by a process of ion-exchange, whereby the calcium and magnesium cations are removed and replaced by other mineral cations, most commonly sodium from salt in the form of sodium chloride, although potassium salts can also be used.
1. Ion-Exchange Water Softening
Salt-based ion-exchange water softeners are the main form of water softener used for domestic household water supplies. They work by removing hardness-causing calcium and magnesium ions from the water and replacing them with sodium or potassium ions that coat the resin beads in the ion-exchange tank.
The system needs to be ‘regenerated’ about once a week to replace the water softening ions that have been expended, and to flush out the hardness ions that have replaced them. Ion-exchange water softeners also have the ability to remove dissolved ferrous (clearwater) iron from the water supply.
This form of iron is usually found in water drawn from deep wells and other groundwater sources. It does not color the water when it is moving, but if the water is left to stand for some time, such as in a toilet bowl, the iron will react with oxygen in the water to form a reddish-brown film or ring.
Each ppm of iron is equivalent to 3 to 4 grains of water hardness, and it is recommended that an ion-exchange water softener should only be used for iron removal if its concentration in the water does not exceed 5 to 6ppm, otherwise an iron filter should be used in conjunction with the water softener.
In addition, if chlorine levels are high, these can lead to the breakdown of resin beads in the water softener, as well as cracking and breakage of the manifold or filter in the water softener tank. To avoid these problems, ensure that your water softener resin tank is filled with 10% cross-link resin beads, which have a better tolerance for chlorine than standard 8% cross-link resin beads.
A further option with ion-exchange water softeners is that of a twin-tank or dual-tank alternating system (this refers to a system having two interconnected ion-exchange tanks in addition to the brine tank), so there is no risk of hard water bypassing the system during the regeneration process.
Most water softeners are fitted with a bypass valve so that water is still available at household faucets while the system is regenerating its resin beads with salt.
Some systems allow a limited reserve of soft water to be held for use during regeneration, but this may not be sufficient. If there is no reserve set, or if it runs out, hard water will flow through the bypass valve into your household water network until the regeneration process has been completed and the water softener comes fully ‘on-line’ again.
If you set your water softener to regenerate in the early hours of the morning and are certain that no household water will be required during this time period, then you won’t benefit from a twin-tank system.
But, if your household water use is irregular during the day and night or if you use water during the night, such as having a shift-worker in the household or a pre-timed laundry washing machine taking advantage of off-peak energy tariffs, then the choice of a twin-tank water softener will ensure that your household water system is protected from ingress of hard water.
When the resin in one of the ion-exchange tanks is approaching saturation and needs regeneration, the system will automatically switch over to the other tank which has full capacity. In this way, you will always have softened water flowing in your household water network.
Iron Pro water softeners are available in dual-tank alternating models with 10% cross-link resin at various capacities, and represent a comprehensive solution for chlorinated water with iron concentrations up to 6ppm.
2. Salt-Free Water Conditioning: Template Assisted Crystallization (TAC) / Nucleation Assisted Crystallization (NAC)
This form of water conditioning is relatively new in commercial usage, and is now available at domestic household scale. The technology has been proven in controlled tests undertaken by the University of Arizona to reduce lime-scale production in hard water by over 96%.
The principle of the process is that microscopic ceramic polymer beads in an active media contain sites or templates that act as anchors for calcium and magnesium hardness ions to accumulate into clusters of nano-crystals. When these clusters have grown to a certain size, but still microscopic, they break away from the beads and are swept back into the water flow.
These crystal clusters are relatively stable and insoluble so they will not attach to other surfaces to form lime-scale. Any scale that does form will be ‘soft scale’ rather than lime-scale, and is easily removed.
TAC has been shown to be effective for water hardness up to 25gpg at a flow rate of 7gpm, but is rated at much higher levels of hardness, up to 75gpg. Unlike ion-exchange systems, the TAC/NAC media needs to be protected from iron by a pre-filter. In addition, the nano-crystals that are formed only last about two days before they break up, so the technology is only suitable for water that is being regularly consumed.
The Aquasana SimplySoft EQ-AST-WH whole house salt-free system uses TAC/NAC technology and has a rated capacity of 6-years.
The system is relatively expensive, in the US$1,300 to US$1,400 range, however, and the conditioner tanks must be replaced in their entirety when their capacity is exhausted. It is supplied with a 5-micron sediment pre-filter which has its own capacity, depending on sediment levels in the water supply.
A TAC/NAC water conditioner system that uses a re-fillable tank can be acquired in the price range between US$700 and US$800. The replaceable media ‘Filtersorb’ TAC/NAC media has an expected lifespan of 3 to 5 years, depending on water hardness.
The advantages of TAC/NAC systems include lower maintenance requirements, simpler installation, better water efficiency (no need regeneration and the accompanying water losses), and less environmental impact.
3. Salt-Free Water Conditioning: Reverse Osmosis (RO)
Reverse osmosis is a process of forcing water through a series of extremely fine filters under pressure, in order to filter all impurities out of the water, down to molecular level.
The resulting product is similar to distilled water, with all chemicals and organic dissolved solids, including hardness-causing calcium and magnesium ions, having been removed. As such, it can be considered a form of water softening.
Most domestic RO systems, however, only cater for one water point in the home, with a dedicated faucet for RO water separate from the rest of the household water system. This means that hard water will still be passing through the water heater and hot water system, producing lime-scale in places where it is most damaging.
Using a light commercial RO system such as the iSpring 500 Gallon/Day Commercial Grade Tankless RO Water Filter System with a storage tank and a delivery pump, you can provide sufficient pure softened water to your whole house for up to 6 people at the recommended average of 75 gallons per person per day. A system such as this one has four pre-filters to remove sediment, iron and chlorine before the water enters the RO chamber, allowing longer and more efficient operation.
There are, however, a few things to bear in mind with an RO system, including the fact that it takes two or more gallons of hard water to produce one gallon of softened water, so water consumption will always be higher than with other systems. In addition, although RO will remove unwanted hardness minerals, it will also remove all other minerals and nourishment from the water.
This water may not be healthy to consume in the long term without re-introducing desirable minerals and salts. Finally, the RO membrane/s will need to be back-washed and cleaned on a regular basis – fortunately the above system will do this automatically.
4. Salt-Free Water Conditioning: Chelation
Chelation is a means of conditioning hardness-causing ions in water so they do not combine with other chemicals in the water to form so-called lime-scale. This process has been used for treating water in commercial applications for several decades, such as in factories, laundries and restaurants, but has only fairly recently become available for domestic scale uses.
The main difference between ion-exchange and chelation is that the latter process does not remove hardness ions from the water, but simply modifies their charge state so that they become inert and less reactive with other chemicals. For this reason, systems using this process are correctly described as ‘water conditioners’ rather than ‘water softeners’.
The advantage of this is that calcium and magnesium ions remain in the conditioned water and are able to provide health benefits when the water is consumed, and there is no increase to the sodium content of the water for those people who are on low-sodium diets for health-related reasons.
Other advantages of this salt-free process are ease of installation, no water wastage, negligible maintenance, sodium use or environmental impact.
Water conditioners use an active ingredient, such as a form of food-grade citric acid or polyphosphate, impregnated in a replaceable cartridge, to condition or ‘sequestrate’ calcium and magnesium hardness ion, as well as those of iron and manganese, so that they will not react with other free ions to form lime-scale.
Any scale that is formed is easily dislodged or removed and, in fact, existing lime-scale is gradually broken down and removed by the crystals that may form. The sequestered ions also do not form ‘soap scum’ and any marks left on glass surfaces can easily be wiped off.
Unfortunately, the conditioning only lasts for a limited time period, and water that is left to stand for several days, or is continuously circulated in a heating system, will tend to lose its ‘conditioning’ and the hardness ions will re-activate. For this reason, water conditioning should only be used for water that will be used within a day or two.
Since salt-free systems do not remove hardness ions from the water, water hardness tests performed on ‘conditioned’ water will show little difference in results from the original ‘hard’ water supply, making it difficult to ascertain the effectiveness of the system.
The most common symptom of an expended water conditioner cartridge is the presence of increasing water hardness in the form of soap scum, so it is best to ensure that the cartridges are replaced promptly and regularly.
The 3M AP904 which has a rated capacity of 100,000 gallons and an expected cartridge replacement period of 12 months is one of the highest capacity salt-free water conditioners available. Unfortunately, the water hardness level at which this system is rated, is not indicated in its literature.
The Aquios FS220 system has a rated capacity of 40,000 gallons with a maximum hardness rating of 22gpg, and an expected cartridge lifespan of 4 to 6 months.
The Nuvo H2O Home system has a rated capacity of 35,000 gallons with a tested hardness rating of 15gpg, and an expected cartridge lifespan of six months.
In terms of value for money, based on the specifications available, the 3M AP904 appears to be the leader in this field, followed by the Aquios FS220 system, with both of these systems also offering chlorine taste and odor reduction.
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