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How do water softeners work?

The traditional salt decalcifier is an anti-scale chemical treatment system. The procedure used to remove lime is based on ion exchange, i.e. calcium and magnesium ions are exchanged for sodium ions. 

Despite solving the problem of lime in the short term, salt decalcifiers bring new problems: the sodium released is a highly polluting and harmful component, both for the health of people and for the facilities.

Operation of the water softener by ion exchange

Traditional decalcifiers use a resin to carry out the ion exchange. This resin is a synthetic polymer which in this case is called cationic resin because it is negatively charged. In this way it attracts positive ions such as calcium and magnesium.

The process of a salt decalcifier consists of two phases, a decalcification phase and a regeneration phase.

1- Decalcification phase

Calcium and magnesium ions are atoms having a positive electrical charge, as do sodium and potassium ions. Ions of the same charge can be exchanged. In the ion exchange process, a granular substance (usually a resin) that is coated with sodium or potassium ions comes into contact with water containing calcium and magnesium ions. Two positively charged sodium or potassium ions are exchanged (released into the water) for every calcium or magnesium ion that is held by the resin. This “exchange or trade” happens because sodium or potassium are loosely held by the resin. In this way, calcium and magnesium ions responsible for hardness are removed from the water, held by the resin, and replaced by sodium or potassium ions in the water. This process makes water “soft”.  Eventually, a point is reached when very few sodium or potassium ions remain on the resin, thus no more calcium or magnesium ions can be removed from the incoming water. The resin at this point is said to be “exhausted” or “spent,” and must be “recharged” or “regenerated.”

This process, however, is a major health problem, as water from taps and showers contains high levels of sodium.

The traditional salt decalcifier modifies the chemical characteristics of the water and causes sodium levels to exceed the limits permitted by European and Spanish regulations: 200 mg/litre. Therefore, the water treated by the salt decalcifiers is neither potable nor suitable for human consumption…

The water softener releases sodium in the same proportion as the captured calcium. The harder the water, the more sodium is released in the facility.

A decalcified water with a high sodium content favours corrosion, which is a problem for installations and domestic appliances.

In addition, corrosion causes the release of toxic heavy metals that are present in installations. Some, such as iron or zinc, are not harmful in small amounts. However, others such as lead and mercury can cause disease over time by accumulating in living organisms.

2- Regeneration phase

This regeneration process is necessary when the resin reaches a saturation point and cannot capture any more calcium ions.

The decalcifier also consists of a tank containing salt dissolved in water. In this cycle, water with a high sodium content is passed through the container containing the resin. In this way there is an exchange between the calcium ions that have adhered to the resin and the sodium ions of the salt, thus regenerating the resin.

The main problem with regeneration is that it leads to higher water consumption. Salt softeners need periodic regeneration of ion exchange resins. They can reject up to 200 litres of water per regeneration. The frequency of regeneration can vary between 4 and 7 times per month. For this reason, water consumption and water bills increase with the salt decalcifier.

On the other hand, the water with a high sodium content that has been used to regenerate the resin is evacuated through the drain, becoming a great source of pollution. Sodium is a very contaminating component and difficult to eliminate.

Types of salt decalcifiers

There are two models of salt decalcifiers:

– Volumetric system: with this system the regeneration of the resin occurs when a certain volume of water passes through the decalcifier.

– Timer system: a chronometric descaler is programmed so that the resin regenerates from time to time. In this way the regeneration will take place independently of the water consumed.

Inconveniences of the traditional decalcifier

Continuos salt supply

The traditional salt decalcifier requires constant maintenance, as salt levels must be checked continuously and sacks of salt must be added regularly. The salt is necessary for the regeneration of the resin.

– Heath risk

Comprehensive maintenance is necessary to reduce bacteriological risks, as there is a danger of bacterial proliferation in aqueous environments and at a certain temperature.

– High maintenance cost

The annual cost of this maintenance is very high, since in addition to the amount of salt used, it is necesarry to take into account the water wasted in each regeneration of the ion exchange resins.

– Water not suitable for irrigation

A high sodium content in irrigation water affects soil permeability and can cause infiltration problems. Excess sodium also causes soil dispersion and disaggregation.

Drinking water legislation

The European Union defines the basic quality standards for water intended for human consumption (for drinking, cooking, preparing food or for other domestic uses), either in its original state or treated. Both European Directive 98/83/EC and Royal Decree 140/2003 set the sodium limit at 200 mg/litre for drinking water.

Under hard or very hard water conditions this maximum level is more likely to be exceeded in water intended for human consumption. This is because the sodium released by the resins during the decalcification phase is added to the sodium contained in the water before it is treated.

Royal Decree 140/2003 also makes reference to the complementary treatment of the quality of water for human consumption and establishes that a house must leave at least one point of water intended for food that does not come from the decalcifier.

Alternative reverse osmosis

If you want to solve the lime stone problem for your whole house a decalcifier might be still  your best option, beside a magnetic pre conditioning of the water. But if you are mainly concerned about your drinking water, reverse osmosis systems like our Osmo is a great alternative. Due to the physical principal of the reverse osmosis membrane the quantity of produced pure water is not suitable for a whole household but more than enough for your daily drinking water demands. The system removes all impurities and dissolved solids from the incoming water and provides the purest water for drinking, cooking and washing of vegetables. For more info about how a reverse osmosis system works check out our blog post here

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