Let me start with explaining what demineralised water is. Demineralised water, also known as demi water, is purified water and is often used in laboratory applications for industrial and scientific purposes. However, also in your everyday life you will encounter applications with demi water.
For example for ironing your clothes with a steam iron, demi water can be used to avoid lime scale in your iron. But it is also used in car wash installations. A thin layer of demi water is sprayed over the car at the end of the car wash program to avoid dried up drops on your car. At the end of this document a few examples of the use of suitable Bronkhorst instruments are given.
Demineralised water versus distilled water
Demineralised water is water that has been purified in such a way that (most of) its mineral- and salt ions are removed. You can think for example of Calcium, Chloride, Sulphate, Magnesium and Sodium. Demineralised water is also known as demi water or deionised water. Demineralised water is generally considered different from distilled water. Distilled water is purified by boiling and re-condensing. In this way salt ions are being removed.
The major difference between demineralised water and distilled water is that distilled water usually has less organic contaminants; deionisation does not remove uncharged molecules such as viruses or bacteria. Demineralised water most times has less mineral ions; this is dependent on the way it is produced. Deionisation has a cleaner production and it leaves behind less scale in the installations it is used in. A point of attention when using this demineralised water is the material of your instruments. Not all material is suited to serve as a piping material for demi-water; this also depends on temperatures that are used.
How is it made?
Demineralised water is produced via three main routes:
- Via Ion-exchange process using Ion exchange resins: Positive ions are replaced by hydrogen ions and negative ions are replaced by hydroxide ions.
- Via Electro-Deionisation also an Ion-exchange process takes place: An electric current is sent through the resins to keep them regenerated. The unwanted ions move away from the reaction surface to the electrodes.
- Via Membrane filtration: most times in multiple steps
To get the right quality of demi-water several stages of demineralization are necessary. The use of membrane filtration in this case has the advantage that in general no chemicals are needed to produce the demi-water (except perhaps for cleaning); the disadvantage is the amount of (electrical) energy consumed by the process.
Demineralised water – common uses
Demineralised water is used for industrial and scientific purposes. You can think of the following applications:
- Laboratory applications and testing
- Wash water for computer chip manufacture
- Automotive uses eg. lead-acid batteries and cooling systems
- Boiler feed
- Laser cutting
- Optimisation of fuel cells
- Steam irons and steam raising applications
- Pharmaceutical manufacturing
- Fire extinguishers
Health Risks of demineralized water
Demineralised water, which is completely filtered of minerals via (electro) ion-exchange, distillation, membrane filtration or other production methods, you would think that it could be used as drinking water. However, as with all things, there are advantages and disadvantages to drinking demineralised water. The advantage is that the minerals that are bad for us have been taken out. There is a lot of documentation available about bad influences of certain minerals on our bodies. The big disadvantage of drinking demineralised water, however, is that demi water takes out also the good minerals from our body and causes a shortage so our health system cannot function properly anymore. Summarised: demi-water should not be used for drinking water as it removes minerals that are needed for a good health.
Some examples of instruments which can be used for demi water
- Thermal mass flow meters, series LIQUI-FLOW
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