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Water softeners are systems that filter hardness-causing minerals such as calcium-carbonate in water by ion exchange method. Especially in industrial systems such as reverse osmosis systems, steam generators and boiler systems, distillation systems, minerals that cause hardness in water are a big problem and soft water is used in these systems. Thanks to the special resin particles in the water softener device, it provides ion exchange between the hardness-causing minerals and sodium-charged resin and removes the hardness that causes lime formation. They are frequently preferred in industrial water treatment projects where there is a hardness problem.

What is a Water Softener?

Water softeners are equipment that removes the ions in the water that cause hardness from the water by ion exchange. Ion exchange is the most commonly used method in domestic and industrial areas as it is a faster and more efficient way compared to other water softening methods. This method involves an ion exchange column made of special resins. The hardness ions in the water entering this column are replaced with sodium ions to remove the hardness in the water. This results in lime-free water, which is described as soft water.

How Does the Water Hardness Removal Process Work?

First, hard water needs to be defined. Hard water by definition is water that contains high amounts of calcium and magnesium ions. It is generally classified as soft water, medium hard water, hard water, and very hard water. In addition to the German and French degrees of hardness, the ppm unit is also used as a unit of measurement. The table below shows the hardness grades according to the measured value.

Degree of HardnessFrench DegreeGerman DegreePPM (CaCo3)
Soft Water0.0-6.0 °f0-3.37 °D0-60.0
Medium Hard Water6.01-12.0 °f3.38-6.74 °D60.1-120.0
Hard Water12.1-18.0 °f6.75-10.0 °D120.1-180.0
Very Hard Water18.1 °f and above10.1 °D and above181 and above

Water softening devices change the hardness-creating mineral ions in the water by ion exchange method through the resin in the water softener. A typical ion exchange reaction takes place as follows.

Ca(HCO3)2 +SAC-Na2↔NaHCO3 +SAC-Ca

During the reaction calcium ions exchange with sodium ions. This is because the resin has a relative selectivity. Below is the relative selectivity ranking of the water softening resin.

Fe3+ → Al3+ → Ba2+ → Sr2+ → Fe2+ → Mn2+ → Ca2+ → Mg2+ → K+ → Na+ → H+ → Li+

A fact that draws attention in this ranking and may cause misperception is that water softeners can also perform ion exchange for ions such as iron, manganese and aluminum. While this is true, water softening systems are regenerated with salt as standard. Since a resin loaded with iron and aluminum ions cannot be regenerated using salt, the water softener device will not be able to remove hardness. Therefore, if these ions are present in the water, a separate iron-manganese filtration must be installed for them or the resin must be regenerated separately using hydrochloric acid and salt, sometimes even in 2 cycles.

What are System Components?

Each component in a water softening system is specifically dimensioned according to the requirements of the water hardness removal process and the connection structures are created accordingly. A system basically consists of a resin column, a sufficient amount of resin, control valves and a salt (brine) tank.

Resin Column

It is the tank that contains the resin and in which the process is operated. It is specially dimensioned according to the capacity requirement. It is manufactured from materials such as FRP, carbon steel, stainless steel. FRP tanks are used in industry with a high weight.

Water Softening Resin

It is the main material for ion exchange. The resin, which is produced according to the type of ion to be retained, replaces the ion to be retained with the ion on itself with its relative selectivity feature and renews itself by releasing the ions it retains during regeneration. A typical water softening resin has a lifetime of 2 to 5 years.

Control Valve

These resin ion exchange devices have processes such as backwashing, regeneration and rinsing at certain intervals. In these processes, operations such as redirecting and reversing the water flow should be carried out. Control valves simplify/automatize these processes and ensure that regeneration is completed properly. As well as purpose-built compact control valves, external valves are also used for external flow diversion.

Salt Tank (Brine Tank)

Salt tanks are the tanks where the brine needed by the softening resin during regeneration is kept ready. When the softener starts salt regeneration, it draws brine from this tank and loads the resin with sodium. When the system is put into service, it replaces ions such as calcium and magnesium in the raw water with sodium ions.

What are the Advantages of Water Softeners?

Resin water softeners are highly effective and efficient in water hardness removal. The use of soft water brings the following advantages.

Energy Saving

Hard water quickly leads to limescale deposits, especially in equipment such as heat exchangers, boilers and steam generators that work with hot water. This not only significantly reduces heat transfer and efficiency, but also significantly increases equipment lifetime.

Cost Savings

Reduced energy consumption and increased equipment lifetime lead to significant cost savings. This will also reduce maintenance/repair costs.

Improvement in Maintenance Periods

Many water powered industrial equipment have low water hardness tolerances. The vast majority work with soft water, but a very few can work with medium hard water. Equipment exposed to calcification should be serviced periodically. With the use of soft water, the time between maintenance intervals will be considerably increased and component damage will be minimized.

What are the Disadvantages of Water Softeners?

Water softeners have many important advantages but also some disadvantages. These are mainly related to installation and operation. In general, the disadvantages can be grouped under the following headings.

Salt Addition and Salt Consumption

Resin water softeners use approximately 1/5 of the amount of salt per regeneration. This salt is used by dissolving in water in brine tanks. When the amount of water or salt in these tanks decreases, it is necessary to add more.

Installation Area

Resin devices for water hardness removal consist of resin columns, brine tanks and other auxiliary components. For the installation of this system, a space equal to the size of the device must be reserved. Since device dimensions are directly linked to capacity, there is no possibility to make the sizing more compact. As the capacity grows, the installation area will gradually increase.

In Which Areas Are Water Softeners Used?

Hardness in water is a major issue for many water use scenarios. For this reason, the usage area of water hardness removal devices is quite wide. Resin water softeners are generally used for the following purposes.

Domestic Use

Hard water causes some problems in domestic use. Water-powered equipment such as washing machines, dishwashers, combi boilers, water heaters, etc. suffer performance loss or damage due to limescale. For this reason, water softening devices are used in domestic use.

Industrial Use

Water is used in many processes in industrial plants. Most industrial equipment treats water as pure as possible. For this reason, water must be properly conditioned before it is delivered to this industrial equipment. Water hardness removal is one of the preliminary steps in this treatment process.

Medical Systems

Many medical devices are designed to work with soft water. For this reason, especially the water used by health equipment must pass through a water softener.

Agriculture Practices

Hard and calcareous water can have a negative impact on plant health. In addition, the tolerance of irrigation and sprinkler systems to hard water is very low in greenhouse applications.

Reverse Osmosis Systems

Water hardness is critical for industrial reverse osmosis systems. Hard water and the lime deposits caused by it cause deposits on the reverse osmosis membranes and this leads to membrane blockage in the short term. Clogged membranes lead to loss of performance and increased energy consumption, making the membranes unusable.

A typical water softening system

Water softening system

Water Softener Selection Criteria

Two important parameters stand out when selecting water softeners. First of all, the expected capacity of the system and the raw water hardness should be determined. With this information and other process-specific information, device size and specifications are determined.

General Use

The amount of resin in industrial water softeners reaches saturation in certain periods depending on the ion exchange capacity of the resin and inlet water hardness. The saturated resin needs to be loaded with sodium again. For this reason, water softening systems are regenerated with brine. During regeneration, the ion exchange reaction shown above is reversed by introducing brine into the system. Thus, the resin is saturated with sodium again and after regeneration, the softening resin is able to exchange calcium-sodium again and give soft water.

During regeneration, a 10% to 20% solution of dissolved sodium chloride, i.e. brine, is used. The amount of brine to be used depends on the amount of resin and the salt content of the solution.

Regeneration of water softening resin generally consists of 3 stages. These stages are as follows:

Backwash: At this stage, the method of giving water from the outlet and disposing it from the inlet is applied, which is also seen in filter types such as sand filter, carbon filter. Thus, the mechanical pressure on the particles in the tank is eliminated and a homogeneous distribution occurs in the tank.

Salt Regeneration : At this stage, brine solution is supplied to the system from the inlet. A certain amount of brine, depending on the amount of resin and brine solution, initiates the ion exchange reaction in the resin in the tank. In salt regeneration, the flow rate must be such that the brine is in contact with the resin for a long enough time. A high flow rate will increase salt consumption by reducing the contact time, while a low flow rate will greatly extend the regeneration time.

Rinsing: At this stage, the brine in the tank is rinsed and the system is made ready for service again. During rinsing, water is supplied normally from the inlet to the system and the water at the outlet is sent to the waste. This period generally varies between 10-20 minutes.

Operating Conditions

A water softening system has an operating procedure that requires continuous active control. Salt tanks should be checked at frequent intervals and the amount of salt should be kept at an adequate level. Again, raw water and soft water samples should be analyzed periodically to check whether there is a change in raw water parameters and whether there is a hardness leakage at the soft water outlet. In addition, inlet/outlet pressure differentials should also be checked to see if there is a blockage in the resin column.

Maintenance Operations

Softeners are devices that do not require a lot of maintenance. Depending on the operating conditions, it is sufficient to perform leakage/leakage control and mechanical damage control at certain intervals. At the end of the resin life, the entire resin must be replaced.


The system consumes some consumables for water hardness removal. The most obvious of these is salt. Salt tanks should have enough salt to ensure a salinity level of at least 15% and this salt should be in the form used in resin systems. In general, tablet salt is the easiest type to store and operate.

Operating Costs

As with any system, water softener systems also have an operating cost. These cost tables are presented under separate headings below.

Water Consumption

Softeners remove some water from the waste with each regeneration. For this reason, a certain amount of water is discharged as waste during operation. The overall water efficiency of such systems is over 90%.

Electric Energy Consumption

By themselves, water hardness removal devices do not consume significant energy. These systems generally consume as much electrical energy as a cell phone.

Consumption of Consumables

The most important cost item of water softeners is salt consumption. It is generally accepted that 1/5 of the resin amount of salt is consumed in each regeneration.