You can build your own water softener

A comparison of decalcifying systems: which method is worthwhile?

Limescale encrustations on the tap and recurring limescale stains on tiles are annoying. The hardness of the water often varies from region to region - are decalcifying systems for private use a solution? You can read here which systems are available, what they are good for and for whom a decalcifying system is useful.

Drinking water is one of the best controlled foods in Germany. However, lime often interferes with the taste and appearance. According to the manufacturer, external devices should be a simple solution - but according to the consumer advice center, these are unnecessary. Even worse: they can worsen the quality of the water.

How does the descaling work?

When treating the water, the systems work with various processes that are more or less effective. Some manufacturers promise real miracles and an additional improvement in water quality. Experts are now warning of dubious methods.

Dubious test procedures

In order to convince potential customers of the poor drinking water quality on site, representatives for water treatment plants use manipulated test strips, the discoloration of which is supposed to prove the alleged pollution of the water. The drinking water in most German households is flawless due to the strict controls. In the opinion of the consumer advice center NRW, additional processing in the household is usually superfluous. If the wrong measures are taken, the water quality can even deteriorate, warn the experts.

Calcareous water is not harmful

Even if advertising promises convey other information: Hard water is not harmful - neither for your health nor for the fittings. The deposits on the tap or in the coffee machine or in the kettle can be easily removed with citric acid. Put a little vinegar water into the fabric softener compartment with every rinse - then your washing machine will not have any problems with limescale.

Nevertheless, very different decalcifying devices are offered at high prices, from simple table water filters to piped filter systems. The consumer advice center NRW has looked at the offers and sums it up: "With more than half of the filters presented, the water quality is talked about badly or the fear of pollutants and diseases is stoked. which should improve the water quality. "

Don't fall for esoteric methods

According to consumer advocates, you should remain skeptical of offers with the terms "harmonization", "vitalization", "levitation", "energizing" and "hexagonal water." explain the experts.

Water softening usually does not make sense

But even if you only want to reduce the lime content, you should carefully consider whether it is worth purchasing a decalcifying system.

Water hardness
The degree of hardness depends on both the calcium and magnesium compounds in the water.
"Soft" water has a hardness range of 0 to 7 degrees of German hardness (dH) (0 to 1.3 mmol CaO / l).
"Hard" water has a hardness range of 14 to 21 degrees dH (2.5 to 3.8 mmol CaO / l):
You can inquire about the hardness of the water from the municipality or the responsible water supplier.

In its drinking water brochure, the Federal Environment Agency also advises against using devices for water softening in the home. They are neither necessary nor useful because hard water is not unhealthy. All additional fixtures in the drinking water installation require regular, professional maintenance, without which the device could contaminate and pollutants "redissolve" into the drinking water.

The Stiftung Warentest and the consumer center NRW argue in the same way and warn of a possible deterioration in water quality.

Which descaling systems are there?

Nevertheless, the prospect of softer water, less detergent consumption and less limescale deposits is so tempting for consumers with particularly hard water that they decide to buy an installation. You can choose between ion exchangers, reverse osmosis or what is known as "physical water treatment".

Decalcification using an ion exchanger

With a decalcifying system that works on the ion exchanger principle, the water actually becomes softer. In this process, the calcium and magnesium ions - i.e. the lime - are removed from the water and exchanged for sodium ions. The decalcification system is integrated into the water supply in the house so that the lime-containing water first flows through the exchanger resin in the system before it reaches the tap or washing machine. Such decalcification systems are available for single-family houses between 1,000 and 2,500 euros.

However, the exchanger resin has to regenerate regularly in order to be able to provide enough sodium ions again. To do this, the system flushes the resin with a brine solution. The lime-forming substances end up in the wastewater while the exchanger resin is refreshed. Therefore, regeneration salt must be topped up regularly. A single family home system usually requires 10 to 15 kilograms of salt per month. The running monthly costs for electricity, salt and additional wastewater are between five and ten euros.

Disadvantage of the ion exchanger in addition to the high price: If the water stands for a long time, germs can multiply. That is why the LGL Bayern recommends systems that also disinfect the ion exchange resin with every regeneration process. In addition, the ion exchange could remove minerals such as magnesium that are desirable from a nutritional point of view. In return, the ion exchange could lead to an increased sodium load in the drinking water.

Water treatment with reverse osmosis

Reverse osmosis systems are also used for water treatment. The water is pressed through a semi-permeable membrane at high pressure. Large molecules such as nitrate, phosphate, heavy metals, and some minerals cannot pass through the membrane and are held back. The consumer advice center points out, however, that the membrane must be rinsed with high water consumption so that it does not clog. To obtain one liter of filtered water, three liters of drinking water would be needed. That leads to high energy and water costs. In addition, the membrane is susceptible to contamination, an aspect that the LGL also considers a "major problem".

Most devices are designed for installation under the sink, so they are not used to treat all of the household water, but only for one tap. Small systems are available for as little as 100 euros. This form of water treatment is often advertised with the supposed health benefit.

Physical limescale converters are mostly ineffective

These methods use magnetic, electromagnetic or high-frequency fields to prevent limescale from being deposited. That sounds very tempting at first, because this method works without chemical additives, but the effectiveness is extremely controversial. According to the consumer advice center, so far only devices based on the principle of "seed crystal formation" are effective.


In the vast majority of cases, drinking water treatment in the household is not necessary. Even with very hard water, you should carefully weigh the costs and benefits. The washing machine and dishwasher can be adjusted to the hardness of the water by adding salt or the detergent dosage, limescale stains can be easily removed with citric acid or vinegar cleaning agents, and if the limescale flakes in the tea are bothersome, it may be cheaper to use a small table filter. However, you should not underestimate the risk of contamination with table-top units. In addition, Stiftung Warentest is not convinced of their ability to soften the water. Out of nine table filters, the best models achieved a "satisfactory" rating in the test.

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