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Lisa Scholl

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Demineralized water ► What makes it so special?

Natural tap water (H2O) cannot always be used. Especially in areas of science, technology and research, water is needed that is free of certain minerals. Then demineralized water, also called demineralized water, is often used. What it is all about and how it is obtained is explained in the following text.

Natural tap water (H2O) cannot always be used. Especially in areas of science, technology and research, water is needed that is free of certain minerals. Then demineralized water, also called demineralized water, is often used. What it is all about and how it is obtained is explained in the following text.


Demineralized water is also referred to as deionized, de- and demineralized, and demineralized water (demineralized water). From the names it can already be deduced that it is pure water from which certain organic and inorganic substances have been removed. Demineralized water is often made from normal tap water.


Demineralized water differs from distilled water because of the degree of purity, but mainly because of the manufacturing processes. To obtain distilled water, water is heated to the boiling point so that it evaporates. The resulting water vapor (condensate) no longer contains organic substances, salts and trace elements . Distilled water is used for steam irons, for example, but mainly in medical facilities and laboratories.

Various processes are used to demineralize water. If only the exchange of ions is carried out, organic impurities, for example bacteria or viruses, remain in it. In order to additionally filter out these and other substances, so-called reverse osmosis systems are to be used. Desalination of water takes place in them through a membrane, which at the same time acts as a filter for other substances.

Basically, demineralized water is a product that has hardly any mineral and salt ions left that are normally found in natural water. They include, for example, calcium, chloride, sulfates, magnesium and sodium.


The advantages of demineralized water are already apparent in the manufacturing process. To produce distilled water, a high amount of energy is required due to the heating process. In addition, lime and other substances are deposited on the machines used for production.

Furthermore, there are differences with regard to the measured values of demineralized and distilled water. This concerns especially the conductivity and the TDS value, which are significantly higher with distilled water. Both values provide information about the total dissolved solids in the water. They include minerals, salts and metals.

If the values are in the low range, the water quality is particularly good. Pure water is characterized by the fact that it is not conductive and water with low TDS tastes very good. Demineralized water can therefore also be drunk.


Demineralized water can be produced in different ways. For example, ion exchangers or reverse osmosis with the appropriate equipment are used. All production processes are aimed at achieving high purity values and meeting the requirements for demineralized water.


This process is characterized by the use of a non-soluble synthetic resin to exchange ions that have the same electrical charge with each other . This is also referred to as desalination. On closer inspection, it is a matter of exchanging the cations and anions that decay independently in the water.

A distinction is therefore made between cation and anion exchangers. The former involves the exchange of cations, such as calcium and magnesium, for hydrogen ions, which is called desalination, or for sodium ions, which causes softening of the water.

Instead, anion exchangers are used to exchange ions that are negatively charged (for example, sulfate and chloride) for hydroxide ions . In a series connection, the cation exchangers are always connected upstream of the anion exchangers, resulting in complete desalination of the water.

In so-called mixed-bed ion exchangers, cation and anion exchange resins are located together in the same pressure vessel. They are constantly mixed with each other using compressed air, resulting in the continuous interlinking of anion and cation exchange.

The products produced by this process are not the same as pure water. If one would like to preserve this, an additional sterilization would have to take place.


Reverse osmosis systems remove even the smallest particles from tap water, depending on the filters used. For this purpose, the natural water is conveyed against a membrane at high pressure. This can be thought of as a filter that allows water to pass through, but traps small particles and impurities. Several filter stages are used, which remove different substances from the water one after the other.

Each reverse osmosis system has at least one pre-filter and one main membrane. A post-filter is also possible, because only through this the filtered water tastes particularly good. So you can also drink osmosis water. Often, reverse osmosis is followed later by desalination. If the water is softened before treatment, this prevents rapid blocking of the membranes in the reverse osmosis system.

Did you know? Osmotic pressure is critical when very small ions are to be retained by the membrane. For example, the osmotic pressure is particularly high in salt water. Little pressure is required for solutions containing staggered micro and macro particles. These have a particle diameter of 0.1 to 1 micrometer.


After reverse osmosis, electrodeionization, also known as EDI, is used at best, because it can be used to achieve low conductivity and silicic acid values . Ion exchange membranes, ion exchange resins and electricity are used for this purpose. The result is water with very high quality.

The EDI is an alternative to the mixed bed exchanger and is widely used in the treatment of boiler feed water in power and heating plants, as well as process water in the electrical industry, hospitals and laboratories.


Pure water can be recognized by the fact that it is not electrically conductive. This is due to the fact that it no longer contains anions and cations that occur in natural water. Conductivity is expressed in S/cm, which means Siemens per centimeter. However, since conductivity can hardly be detected in purified water, it is only microsiemens/cm (µS/cm). Such a measurement can be easily performed at home if a TDS meter is available. The conductivity should not exceed 5 µS/cm for demineralized water.

It is a weak acid as it has a pH of about 5.0. The pH value in water depends on the temperature and the proportion of dissolved oxygen and carbon dioxide.


Demineralized water is mainly used in industry and science. Basically, it is used wherever deposits are to be avoided that may occur due to natural water or conductivity is not desired. Fields of application for deionized water can be found here:

● in the laboratory and during the performance of tests

● in car wash facilities

● as washing water for computer chip production

● in cooling systems

● at the boiler feed

● when optimizing fuel cells

● In steam irons and steam generator applications.

● in production processes in the pharmaceutical industry

● in the cosmetics industry

● in the restoration of old books and writings.

● in fire extinguishers

Demineralized water is also excellent for cleaning. This is due to the fact that the pH of the water adjusts to that of the environment. As a result, it is considered a good solvent.


Demineralized water can certainly be drunk. The removal of minerals, which are also not good for the body, is even an advantage. However, the process also removes the substances that are important for us. Furthermore, drinking demineralized water can disturb the water balance of our cells, which is not harmless with regard to our own health.

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