Water softening

Water softening protects pipes from limescale and corrosion

Water softening is a key component of drinking and process water treatment. It protects pipes, equipment and systems from limescale deposits and corrosion. The following section outlines the basics, definitions and common methods for reducing water hardness.

1. Why is water softened?

Water is softened to prevent corrosion and deposits on pipes and water-carrying parts. Reducing water hardness helps to prevent damage and efficiency losses in technical systems.

2. Basics of water hardness

The hardness of water is mainly caused by calcium and magnesium ions. Although hardness values are no longer parameters that must be tested in the Drinking Water Ordinance, their determination is still relevant for technical applications.

2.1 Definition of German water hardness

• 1 °dH = 0.18 mmol/l alkaline earth metals
• 1 °dH = 0.36 mval/l alkaline earth metals
• 1 °dH = 1.00 mg/l calcium oxide (CaO)
• 1 °dH = 7.14 mg/l calcium (Ca)

2.2 Hardness ranges according to the German Detergent Act

3. Methods of softening

3.1 Ion exchange method

In ion exchange, calcium and magnesium ions are replaced by sodium ions. Strongly acidic cation exchangers in the Na form are used. To regenerate the resin, a salt brine is passed over the resin.

• Regeneration takes place automatically.
• Dual systems enable softening even during regeneration.
• Water filters and DVGW-certified components are required in accordance with DIN EN 1717.

Process limits:

Approximately 8.2 mg of sodium per litre is required to reduce the hardness by 1 °dH. The sodium limit according to the Drinking Water Ordinance is 200 mg/l.

3.2 Hardness stabilisation

Phosphate-containing active ingredients prevent the precipitation of hardness-forming substances. Up to 90% hardness stabilisation is possible.

• Suitable for private use
• Effectiveness limited by temperature (usually max. 60 °C)

3.3 Membrane process (nanofiltration)

With nanofiltration systems, hardness can be reduced to approx. 50% of the raw water hardness. They work in a similar way to reverse osmosis systems and retain calcium and magnesium compounds.

• Water analysis is essential.
• Module selection crucial for efficiency

4. Corrosion protection (nanofiltration)

When using metallic pipes, suitable corrosion protection is essential. Recommendations can only be made on the basis of a specific water analysis.