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Aquaclinics - Demineralised water or demi-water

Demineralised water (demi-water, demin water, deionised water) is water from which all ions (salts, minerals) have been removed. When demineralised water is purified even further and other substances are also removed from the water, such as suspended and/or organic substances, the result is ultra pure water (UPW).

Distilled water or aqua dest is very pure water from which many organic substances have been removed, in addition to all anorganic salts, by means of distillation. Water is sometimes subjected to double distillation (double dist) to achieve the highest possible level of purity.

Thanks to the presence of positive ions and negative ions, water inherently conducts electrical current. This is called ‘conductivity’ and is expressed in ‘Siemens per metre’. For greater accuracy, the unit ‘micro-Siemens per centimetre’ is usually used (µS/cm). The conductivity of drinking water is usually between 300 and 800 µS/cm. Demi-water contains very few ions and it therefore has low conductivity. Demi-water does not have a defined quality. In popular speech, we refer to demi-water as having a certain quality when its conductivity is less than 5 µS/cm. However, conductivity of < 0.2 µS/cm is usual. If the level of conductivity is lower, it is no longer expressed as conductivity (because electricity is no longer being conducted) but as resistance. This is the reciprocal value (1/x) of the conductivity (0.2 µS/cm 5M?). In the case of ultra pure water, we describe the value as > megaOhm water.


Various techniques are used to remove salts from water, of which the following are the best known:

- Evaporation/combined with condensation. Distillation (Wikipedia link)

- Ion exchangers
  • Positive ion exchanger
  • Negative ion exchanger
  • Mixed bed ion exchanger
- Reverse osmosis (RO)

- Continuous de-ionisation