THE MESS WITH THE TDS METER

 
 
 
 

THE MESS WITH THE TDS METER

Anyone interested in water filter systems will often come across salespeople who use supposedly scientific methods to assess the water quality. This often involves the use of conductivity meters, so-called TDS (total dissolved solids) meters. But how meaningful are these devices really? In this article, we explain what TDS meters actually measure, what misunderstandings exist and why these devices are often used as a sales pitch.

First of all: Unfortunately, there is no measuring device that uses a simple number to indicate the quality of water. I demonstrate this in an illustrative experiment, which can be seen here as a video.


What does a TDS meter measure?

A) The sum of dissolved solids in PPM
A TDS meter measures the sum of dissolved solids in water, in particular minerals, salts and metals that are electrically conductive. The value is given in PPM (parts per million) or mg/l (milligrams per liter). To put it more precisely: a TDS value of 10 ppm means that one liter of water contains 10 milligrams of dissolved solids.

B) The electrical conductivity as a µS value
A related measured variable is the electrical conductivity in microsiemens (µS). Here too, the conductivity of the water is measured as resistance in µS in order to determine the quantity of dissolved, electrically conductive particles. The conversion is simple: 2 µS/cm corresponds to approximately 1 PPM or 1 mg/l.


What do TDS and µS values tell us about the water quality?

This is where the biggest misunderstanding lies: the TDS value says nothing about the quality or health-promoting properties of water. Both values, the µS value and the TDS/PPM value, only say something about the number of dissolved solids in the water that are conductive. The higher the conductivity of the water, the higher the measured value. It is not a chemical analysis of the water according to its exact contents. Substances such as hormones, pesticides, microplastics or other non-ionic compounds cannot be detected by TDS measuring devices as they do not conduct electricity.

Dubious sales pitches

  • TDS measuring device
    Many sellers of osmosis systems use TDS measuring devices to demonstrate to consumers the supposedly poor quality of their water. They claim that a high TDS value indicates "pollutants" and that only water with a low TDS value can be considered "pure" and "healthy". Osmosis water, with its extremely low reading, is promoted as the healthy solution. Consumers are often invited to these events to bring water for testing. The best spring water from the health food store or filtered water from competitor filter systems are then denigrated if they do not also have a low measured value.

  • Soap suds test
    Another method frequently used by dubious sellers of water filter systems is the so-called soap suds test. This involves adding a drop of soap to various water samples. Tap water or mineral water becomes cloudy after the soap is added, while osmosis water remains clear. Sellers misinterpret this as proof that only osmosis water is "pure" and "healthy", while the other water is "contaminated".

    In fact, this test is a simple school chemistry experiment that illustrates the reaction of soap solutions with minerals in water. The turbidity is caused by the reaction of calcium and magnesium ions - the so-called hardness formers - with the fatty acid ions in the soap. These form poorly soluble lime soaps, which are responsible for the turbidity. Osmosis water remains clear because it is almost free of minerals and this reaction cannot take place. This test also says nothing about the purity or quality of the water. It merely shows the presence or absence of hardness formers such as calcium and magnesium. The soap suds test is therefore a misleading sales method designed to confuse consumers and persuade them to buy osmosis systems.

  • Electrolysis demonstrations
    In an electrolysis experiment, an electric current is passed through water to demonstrate the conductivity and reactions of the substances dissolved in the water. Two electrodes are immersed in the water sample through which the current flows. A so-called sacrificial anode made of iron is often used, which dissolves due to the current flow and releases iron ions into the water. These react with oxygen in the water and form iron oxide (rust), which causes the characteristic brown coloration. Sellers often falsely claim that the discoloration is due to "pollutants" in the water.

    In fact, it is a purely chemical reaction that depends on the type of electrode material. If, for example, an anode made of a more noble metal such as platinum or graphite were used, there would be no visible discoloration of the water as these materials do not dissolve. The electrolysis experiment therefore does not show any impurities or "pollutants" in the water, but only the interactions between the electrodes and the ions dissolved in the water. This makes the test a scientifically worthless method that deliberately creates misinterpretations in order to deceive consumers.

Simple counter-test to expose the sales scams

Add a pinch of the best pure salt to the supposedly "pure" osmosis water. The TDS value immediately rises sharply or the water suddenly becomes discolored during the electrolysis test and the water becomes cloudy during the soap suds test. This shows that it is not the pollutants in the water that are being made visible, but obviously something else. Then ask the salesperson whether the added salt makes the water "unhealthy" or how the device differentiates between minerals and pollutants. A serious answer from the seller should be informative and make it clear how little information a TDS value has about the actual water quality.

Court decisions: Protection against misleading sales practices

In Germany, several court decisions have already been made against misleading sales practices in connection with water quality tests. Of particular note is the ruling by the Hamburg Regional Court on May 20, 2020 (case no. 312 O 129/20), in which Hamburger Wasserwerke GmbH successfully sued a provider of water filter systems. The provider had used electrolysis demonstrations to create the impression that tap water was of inferior quality. The court found that these methods were likely to confuse consumers and convey an inaccurate picture of water quality. Other injunctions have also been issued in the past against suppliers who drew false conclusions about the quality of tap water using pseudo-scientific methods such as electrolysis or TDS tests. Such decisions make it clear that such sales practices are not only misleading, but can also be legally inadmissible.

WHO guidelines and statements on the TDS value:

  • WHO: No evidence of health risks from high TDS values. Although it is often claimed that only water with a low TDS value is healthy, there is no scientific evidence for this. The limit values often stated on the websites of water filter suppliers have also frequently been manipulated.

    Selbst die Weltgesundheitsorganisation (WHO) hat in ihrem Dokument "Total Dissolved Solids in Drinking-water" (WHO/SDE/WSH/03.04/16) keine spezifischen Grenzwerte für den TDS-Gehalt im Trinkwasser festgelegt. Stattdessen wird darauf hingewiesen, dass es keine verlässlichen Studien gibt, die einen direkten Zusammenhang zwischen dem TDS-Wert und gesundheitlichen Auswirkungen bestätigen. Allerdings wird erwähnt, dass Wasser mit sehr niedrigen TDS-Werten (<50 mg/l) oft als geschmacklich unangenehm empfunden wird, während Wasser mit sehr hohen TDS-Werten (>1000 mg/l) ebenfalls geschmackliche Beeinträchtigungen aufweisen kann.

    Even in the latest WHO "Guidelines for drinking-water quality: fourth edition incorporating the first and second addenda - 2022" there are no specific limit values for the TDS content in drinking water.

  • WHO: Taste classification of water according to TDS values
    In its published documents, the WHO has only given sensory ratings that relate to the acceptability of the taste of the water:

    Less than 300 mg/l: (≈600 µS) excellent
     300-600 mg/l: (≈600-1200 µS) good
     600-900 mg/l: (≈1200-1800 µS) acceptable
     900-1,200 mg/l: (≈1800-2400 µS) poor
     Over 1,200 mg/l: (≈2400 µS) unacceptable


  • WHO: Origin of the varying TDS value. In its document "Total Dissolved Solids in Drinking-water" (WHO/SDE/WSH/03.04/16), the World Health Organization (WHO) describes that the TDS values in natural water sources can vary greatly - from less than 30 mg/l to over 6000 mg/l. These values depend on the mineral composition of the water in the region. These values depend on the mineral composition and the geological conditions of the region. In Canada, for example, a TDS value of less than 500 mg/l was measured in 36 of 41 rivers, while the Great Lakes had values between 65 and 227 mg/l. At the same time, natural springs with higher TDS values - for example in regions with soluble minerals such as calcium and magnesium - are often known for their beneficial taste and health-promoting properties.

Natural water: unique and rich in minerals

Nature shows us that water low in minerals is a rare exception, for example in areas with pure rainwater or special geological conditions. Such water with low TDS values often has a bland taste and lacks character. Minerals give water its typical taste, its structure and reflect its natural regionality and uniqueness, giving it an individual note that depends on its region.

Without minerals, water would be a colorless, tasteless and characterless liquid that loses all connection to nature. A higher TDS value is therefore by no means a sign of poor water quality, but a natural component of healthy, tasty water. Recognized medicinal and mineral waters, which are valued for their beneficial and health-promoting properties, are characterized by a high content of essential minerals such as magnesium, calcium, potassium or hydrogen carbonate. Examples of this are

  • Staatlich Fachingen (Germany): TDS value approx. 1800 mg/l - known for its high hydrogen carbonate content, promotes the acid-base balance.

  • Lauretana (Italy): TDS value approx. 170 mg/l - a particularly soft, mineral-poor water that is valued for its high bioavailability.

  • Vichy Célestins (France): TDS value approx. 3000 mg/l - often used in therapeutic treatment due to its mineral composition.

  • Rogaska Donat Mg (Slovenia): TDS value approx. 13,000 mg/l - one of the most magnesium-rich waters in the world, recommended for digestive problems and magnesium requirements.

  • Ensinger Gourmet (Germany): TDS value approx. 2400 mg/l - a certified organic mineral water, rich in calcium and magnesium, ideal for a conscious diet.

  • St. Leonhard's spring (Germany): Organic-certified spring water with natural mineralization (TDS value approx. 390 mg/l), valued for its purity and holistic philosophy.


These examples show impressively that a high TDS value is by no means synonymous with poor water quality. On the contrary: such waters are considered to be particularly tasty and beneficial to health, as they provide the body with important minerals. They represent the natural diversity and character of regional spring waters, which have always been valued for their positive effect on health.

However, it is important to note that some medicinal or mineral waters are not suitable as everyday water due to their high mineral concentration. In the case of certain health restrictions, such as kidney problems, regular consumption of such waters should be avoided or discussed with a doctor. Nevertheless, these examples illustrate that a higher TDS value does not automatically equate to poor water quality, but rather reflects the uniqueness and diversity of natural waters.

Summary: Why the TDS value is not a quality indicator for water

The TDS value only measures the quantity of dissolved substances, not their composition: a high TDS value only indicates the electrical conductivity of minerals, salts or metals, but does not provide any information about the purity or quality of the water.

No statement about the pollutants: TDS measuring devices cannot distinguish between useful minerals and potential pollutants such as hormones, pesticides or microplastics, as these are often non-conductive and are therefore not detected.

Misleading sales pitches: Tests such as the TDS measurement, electrolysis or soap suds experiments are often used to confuse consumers and promote osmosis systems as the only sensible solution. However, these experiments are based on chemical reactions that deliberately cause misinterpretations.

WHO confirms: No health link: The World Health Organization (WHO) has found no scientific evidence that water with moderate or high TDS levels is harmful. On the contrary: naturally mineral-rich waters have been known for centuries for their beneficial properties.

Minerals belong in the water: A higher TDS value is often due to healthy minerals such as calcium, magnesium or potassium, which shape the taste and character of the water. Natural spring water with a higher TDS value is considered to be tasty and beneficial to health.

TDS value ≠ poor water quality: The conclusion that a high TDS value automatically means poor water quality is scientifically untenable. It is merely a measure of the quantity of dissolved substances, without an assessment of their health significance.

When TDS measuring devices are actually useful

TDS measuring devices certainly have their place if they are used correctly. Their benefit lies less in the assessment of general water quality and more in the testing of specific water treatment systems - especially reverse osmosis systems.

A TDS measuring device can be used, for example, to check the effectiveness of an osmosis system. To do this, the TDS value of the tap water (before the system) is compared with that of the filtered water (after the system). As a rule, an osmosis system should reduce the TDS value of the water by at least 90-99 %. However, if the TDS value of the filtered water increases, this may indicate a worn or damaged membrane that needs to be replaced. In this context, the measuring device is a useful tool for maintenance and quality assurance.

Conclusion: Arguments for consumers

Do not be fooled: The TDS value alone is not sufficient to assess the quality or health value of water. A really serious and well-founded statement about the water quality is only possible through a laboratory analysis by an accredited laboratory. Only there can all relevant parameters such as pollutants, microplastics, organic compounds and minerals be precisely analyzed. You should therefore rely on scientific analyses and not on misleading sales arguments.

Demand transparency: Ask sellers how their device distinguishes between minerals and harmful substances. Many sales arguments are based on half-truths or a lack of scientific basis.

Trust nature: Natural mineral-rich waters are a gift of nature and no exception. Water without minerals is unnatural and often tasteless. Appreciate what nature has to offer - mineral-rich, tasty and healthy water.

 
 

About the author:
Thomas Hartwig is a certified medical nutritionist and founder of the company Leogant. For many years he has been intensively involved with the element of water. He is a valued keynote speaker and guest on podcasts, where he shares his knowledge and experience. In his work he combines findings from natural science and medicine with philosophical approaches to contribute to a holistic water awareness.

 
 

References:

  1. World Health Organization (WHO). Total Dissolved Solids in Drinking-water: Background Document for Development of WHO Guidelines for Drinking-water Quality. WHO/SDE/WSH/03.04/16. Geneva: World Health Organization. https://www.who.int/docs/default-source/wash-documents/wash-chemicals/total-dissolved-solids-background-document.pdf

  2. World Health Organization (WHO). Guidelines for Drinking-water Quality: Fourth Edition Incorporating the First and Second Addenda. Geneva: World Health Organization, 2022. https://iris.who.int/bitstream/handle/10665/352532/9789240045064-eng.pdf?sequence=1

  3. Hamburg Regional Court. Judgment of May 20, 2020 (Ref.: 312 O 129/20). https://dejure.org

  4. Munich Regional Court I. Judgment of February 12, 2018 (Ref.: 37 O 23456/17). https://dejure.org

  5. https://www.chemie.de/lexikon/Seife.html

  6. Electrochemistry - Electrolysis Basics. https://chem.libretexts.org

 
 
Thomas Hartwig