Chemical water treatment - what is being done?

In order to achieve a quality of water according to the quality requirements of the Drinking Water Ordinance, different procedures are necessary. Which procedures can be expected for the chemical treatment processes, and what they serve, explained in detail this contribution.

Different processes in water treatment

In addition to biological processes, which are hardly used in the treatment of drinking water, and the physical processes (including the mechanical processes), there are also chemical treatment processes.

Essentially, these are:

  • oxidation
  • disinfection
  • Decarbonization / softening
  • ion exchange

In addition, there are some special processes, such as ozonation, which not only disinfects the water, but also simultaneously oxidizes iron and manganese and removes it.


Oxidation is a chemical reaction in which a substance emits electrons. He is changed by it. Another substance absorbs this released electron and is thereby also changed. Oxidation reactions are common in chemistry.

They determine the changing interaction of substances. Every oxidation always requires a reduction. It concerns the substance that absorbs the emitted electron.

For example, to be able to remove iron from the water, first the iron compounds which are dissolved in the water must be oxidized. The same applies to the manganese present in the water. Substances that cause oxidation are called oxidants.


For the disinfection of drinking water according to the Drinking Water Ordinance only certain substances are permitted. In the main, this is chlorine and chlorine dioxide, but also some other substances, such as ozone, are approved according to the Drinking Water Ordinance for disinfection.

For all substances added, however, their use must be technically or hygienically absolutely necessary. In addition, there is a strict minimization requirement for use.

Decarbonization / softening

In decarbonization, only the carbonate hardness is reduced, but in the softening, the total water hardness. Both methods are only used if the water hardness of the raw water makes this necessary.

ion exchange

Using ion exchangers, certain substances can be removed from the water and replaced with others. One example of this is ion exchange systems for water softening, but the principle also works with other substances.

Tips & Tricks

With good starting water, often only the adjustment of the water parameters (pH value and similar technical control values) is necessary.

Video Board: Water Treatment | Coagulation Chemistry Basics