Anyone using a TDS meter to measure the quality of drinking water is probably barking up the wrong tree. Due to the nature of the test, the TDS value provides information about the amount of minerals, salts and metals in drinking water that exhibit electrical conductivity.
Substances such as calcium, magnesium and iron are also recorded, but are harmless to humans. Heavy metal residues, on the other hand, are dangerous. The TDS value only indicates the amount of dissolved solids in the water, which is called “Total Dissolved Solids”, but not which substances are actually contained.
Absolutely pure water cannot conduct electricity because the water molecule is neutral and has neither a positive nor a negative charge. The measured quantity microsiemens (µS) indicates the electrical conductivity of a substance. The dissolved conductive particles can be converted to the sum in the common unit mg/l (milligrams per liter) or in English ppm (parts per million). The following conversion key is used: 1.2 µS/cm = 1 ppm = 1 mg/l.
HOW IS THE TDS VALUE MEASURED?
A TDS meter is a small, easy-to-use handheld device and is also suitable for home use. It provides simple, easy-to-read measurements when reference values are available. Many amateur chemists also order these devices via the Internet, which are becoming increasingly popular due to their ease of use and user-friendliness. A value of 40 ppm means that out of one million particles, 40 ions are dissolved and the rest (= 999 960) consists of water molecules.
The TDS value does not allow any conclusions to be drawn about the type of dissolved substances . A high TDS value ( ≥ 400 ppm) simply indicates that there are more minerals, salts or metals in the drinking water. The TDS value is a purely quantitative measure of the amount of dissolved substances in the water. It cannot be used to determine whether these substances are beneficial or harmful to health.
Not only the average measured values in German mineral and tap water cause more confusion than clarity, but also the officially set limits of the EU, the USA and the WHO.
TDS AVERAGE VALUES (PPM) IN GERMAN WATER
Although the TDS value cannot tell much about the water quality, there are nevertheless limit values for it. Consumers can use one of the many ppm tables to see where their tap water falls on the TDS spectrum.
The following table shows how much TDS is found in German tap and mineral water. These vary depending on the type of water or origin. However, conductivity does not indicate how healthy the water actually is.
It turns out that there is serious disagreement about the maximum recommended or allowable levels. But Germany also bases water quality under the Drinking Water Ordinance on a much broader range of criteria than just the TDS value.
LIMITS SET BY THE EU, THE USA AND THE WHO
If you look at the limits set by other countries and the WHO, you will see that they differ greatly.
It is wrong to say that only water with a very low TDS value (≤100 ppm) is beneficial to health. It’s the type of substance that matters, not the amount. Even the smallest amounts of heavy metals, such as copper or lead, can be extremely harmful.
Substances hazardous to health that may be present in drinking water but have no electrical conductivity cannot be measured by the TDS value. These include substances such as:
✅ Germs and bacteria
✅ Drug residues
These substances can also be harmful to health in higher quantities or over a longer period of time. It is therefore important that these substances are also detected during quality checks and filtered out if necessary. Since a TDS value cannot provide information about these substances, other tests may need to be used to determine the potability of the water.
DOES A LOW PPM LEVEL MEAN HEALTHY WATER?
As mentioned earlier, low TDS or ppm levels are often associated with healthy water. This association is not completely wrong, but it contains a fallacy. Thus, it is possible to find out how many solids are in the water, but not what they are.
A PINCH OF SALT ALONE BRINGS A HIGH PPM VALUE
A water with a ppm level of 800 may have a high concentration of metals such as copper or lead. Health would of course be extremely endangered by this. On the other hand, water with a value of 0 ppm can also be brought to this 800 by adding a pinch of common salt. Even if slightly salty water is not particularly tasty, it is not harmful to health or of poor quality. Nevertheless, a TDS measurement conveys just that.
DO DISSOLVED SOLIDS CAUSE POOR QUALITY TAP WATER?
The substances that drive up TDS levels are now being discussed again. In addition to heavy metals such as copper and lead, minerals such as sodium, magnesium and calcium are also considered.
On the one hand, humans undoubtedly need these minerals. On the other hand, it is claimed that these substances burden the body and should be better filtered. But a large glass of tap water contains about as much magnesium and calcium as 100 g of Emmental cheese. A healthy and balanced diet in itself covers the need for minerals and trace elements.
So whether filtering tap water with a moderately high ppm level is necessary is irrelevant from a health perspective. However, in any case, all substances in the water have an impact on the taste.
WHICH POLLUTANTS ARE NOT INCLUDED IN THE TDS VALUE?
It is now obvious that a TDS value, a microsiemens water level, or a ppm measurement do not provide information about water quality. Contained chloride, carbonates or sulfate-containing water indicate conductivity. Since all these measurements are based on conductivity, non-conductive substances remain undetected.
Many measurements, as mentioned earlier, have difficulty detecting pollutants such as heavy metals, pesticides, fungicides, hormones, drug residues, and last but not least, microplastics, and differentiating them from non-harmful substances.
For example, pesticides and fungicides enter groundwater or the atmosphere and ultimately the water cycle via agriculture, as do microplastics, hormonal substances and improperly disposed medicines that have a negative impact on people’s health.
The water cycle has long been a global environmental problem, driven primarily by microplastic pollution. For example, researchers have already found tiny pieces of plastic at the North Pole, where they are far from their point of origin.
The eco-balance of tap water is also significantly better than that of mineral water when it comes to drinking water. Bottle production, bottle cleaning, filling plants, transport, return transport in the case of reusable bottles or disposal in the case of disposable bottles are not necessary with water from the tap.
Mineral water requires more than a thousand times the energy to produce the same amount. Water from abroad or from distant regions has a particularly poor environmental balance . Even regionally bottled mineral water from a nearby supplier is 100 times less environmentally friendly than tap water.
DRUGS AS A RISK IN DRINKING WATER
German wastewater treatment plants act as an excellent filtration system due to drinking water regulations, but absolute safety and efficiency are not guaranteed. This is partly due to the ever-growing list of substances and diversity, and partly due to the fact that certain drugs, such asdiclofenac, are very difficult to biodegrade and persist for a long time.
Experts therefore repeatedly warn against disposing of medicines down the toilet, as this directly harms both the environment and people. But residues also enter the water cycle during showering, hand washing or normal toilet use. As the aging population takes more and more medications, this can lead to significant risk.
WHAT CAN A TDS MEASUREMENT BE USEFUL FOR THEN?
After the initial setup of the system, the TDS value can be used to determine whether the filter is functioning properly or has been connected correctly. However, this value does not provide information about the water quality. Rather, water quality is determined by which substances are dissolved in drinking water and in what concentrations.
The fact that non-conductive substances are also present in water can lead to misleading assessments of water quality based on TDS values. Pharmaceutical residues or pesticides, for example, which have entered the private water cycle either via wastewater from private households or from agriculture, cannot be detected in drinking water by a TDS measurement. A good TDS value alone is therefore not sufficient to make a reliable statement about the water quality.
Reverse osmosis systems are particularly susceptible to fouling if the filters are not changed regularly, resulting in reduced filter performance. This forces the membrane to provide higher filtration performance, which shortens its service life. As a result, the more expensive membranes have to be replaced prematurely.
Therefore, it is also possible to follow the development of the osmosis water by means of a TDS measurement and to recognize when it is time to change the filter and membranes. The TDS value in the osmosis water should never exceed 30.
HOW CAN YOU FIND OUT THE REAL QUALITY OF DRINKING WATER?
A TDS measurement can be used to estimate the conductivity of drinking water in microsiemens or ppm. However, for the reasons already stated, this should only be considered a rough indicator of water quality. For example, demineralized water can deceptively appear to be of good quality and drinkable with low ppm levels in these measurements. However, contaminants may still be present in the sample. Humans also need certain minerals in drinking water to maintain their health.
Information about the quality of drinking water can be obtained from the health department or water supplier before consumption. According to the German Drinking Water Ordinance, § 21, paragraph 1, suppliers are obliged to provide analytical data and quality information. These are often provided online or, if necessary, upon request.
All water suppliers provide information about their service area. But the quality of water flowing through a household’s water meter can be affected by the condition of the household plumbing. In addition, domestic wells are not tested, so consumers there are on their own.
SIMPLE MEASUREMENT OF THE PH VALUE
The pH value of the water is more decisive for its quality. Acidic water with a pH of less than 7.0 absorbs copper. So if the supplier provides acidic water and copper pipes are used in the house, the water quality will be affected.
Either the pH value specified by the water supplier or a litmus test can be used to determine the pH value. Litmus paper is readily available both online and in pharmacies. A strip of litmus paper is dipped in water, and after a few moments the pH of the water can be seen from the color. It also provides information on water hardness, chlorine content, iron, nitrate, nitrite and alkalinity.
FURTHER MEASUREMENT DATA ON DRINKING WATER QUALITY
In addition to pH, there are other parameters used by the federal government to measure drinking water quality. These are:
The water must meet consumer requirements for odor, turbidity, and color , and must not show any unusual changes.
One liter of drinking water should contain no more than 50 mg of nitrate and no more than 2 mg of copper, 0.02 mg of nickel and 0.01 mg of lead.
No more than 0.1 µg of any single pesticide may be present in a liter of drinking water, and the total concentration of all pesticides may not exceed 0.5 µg.
No Escherichia coli, enterococci or coliform bacteria should be present in 100 milliliters (ml) of water.
At 22 °C, tap water must not contain more than 20 colony forming units per ml.
ANALYSIS BY SERVICE PROVIDER
However, all the measurements, tests, and information options mentioned so far remain uncertain to some degree. This is because the drinking water ordinance only applies up to the water meter. However, the tap water in your own home can be decisively influenced by the installations.
The only way to ensure the purity of the water is to have it tested by a reputable laboratory or the water supplier. A water analysis requires only a tiny sample of tap water, but the cost and scope of the analysis varies.
However, a water analysis is also not always representative of water quality, as it only provides a single snapshot. It can likewise test only a small fraction of all potential contaminants and offers no long-term protection.
There are now numerous suppliers of water analysis and water tests. Water suppliers sometimes offer this service, but since they do not test for all substances, a special lead test should be done, especially if pregnant women or children live in the household.
QUALITY OF MINERAL WATER
The quality of mineral waters is frequently evaluated by Stiftung Warentest, and the results are often surprising. Of the 30 mineral waters tested, none received the grade “very good,” eleven were rated “good,” and most received the grade “satisfactory.” One of the mineral waters was rated “sufficient”.
Traces of agricultural, industrial and domestic wastewater were found in some of the waters. Thus, sweeteners, corrosion inhibitors and pesticide degradation products were detected.
In addition, acetaldehyde, which readily dissolves from the plastic especially during prolonged storage and at higher temperatures, was also discovered in bottled mineral water in PET plastic bottles. However, according to Stiftung Warentest, all the substances detected are still harmless to health at low levels.
However, the mineral waters do not live up to their image, and the prices are usually excessively high. Despite its name, mineral water does not always deliver the minerals it promises.
Testers claim that tap water in some major cities contains significantly more minerals. In Berlin, for example, drinking water contains much more calcium than many mineral waters. In Munich, the same would apply to magnesium. Anyone who considers a high mineral content to be crucial should study the information on the bottled water carefully and compare it with easily accessible water analysis results of the local tap water.
HOW TO IMPROVE THE WATER QUALITY?
In Germany, anyone who pays for a comprehensive water analysis usually receives a result that complies with the Drinking Water Ordinance. The reason is that lead pipes are hardly used anymore and water suppliers ensure the right acidity level for copper pipes .
Depending on the region and living situation, limit values may of course be exceeded . For domestic wells or self-converted piping systems, the responsibility lies with the user. These consumers in particular benefit from a water filter, although it can mean more safety for everyone.
So instead of measuring water quality first and assessing TDS and ppm, it pays to improve drinking water directly. It guarantees, on the one hand, that the water precipitates with a low ppm value and, on the other hand, that pollutants are removed as much as possible.
So if you choose a filter system, you can not only save money, but also increase the already excellent quality of tap water. The most suitable type of filtration process depends on local conditions. There are sediment filters, activated carbon filters, ion exchangers, membrane/reverse osmosis filters, distillation units and microfilters to meet different needs.
In high-quality filter systems, different filter types are connected in series to achieve a particularly high filter performance. All coarse and fine pollutants such as chlorine, trihalomethanes, fluorides, herbicides and pesticides can be removed by activated carbon filters.
A reverse osmosis filter is also able to reliably filter out bacteria, viruses and other substances that can pass through an activated carbon filter. It can also be used to easily remove lime and minerals.
Unlike mineral water, whose mineral composition depends on the source, the mineral content of filtered water can be easily improved. In good filter systems, for example, an osmosis filter adds important minerals such as potassium, calcium, magnesium and sodium.
WATER FILTER FOR BETTER TASTE AND LESS RISK
It is important to mention again that business, industry, the pharmaceutical industry and society as a whole are constantly and continuously introducing a variety of substances into the great water cycle. Therefore, the responsible institutions cannot guarantee absolute freedom from risk for consumers.
By using a private water filter in the home, users can also benefit personally. After all, in addition to the support in this area, users are also doing something good for themselves in terms of taste. Many people already know the difference in taste between tap water in the big city and in rural areas. Properly filtered water is once again a whole new experience in this respect.
Many users already appreciate this and would hardly return to unfiltered tap water. This is not even necessary, because there are so many practical options, such as on-table, under-table or outdoor filters.
FREQUENTLY ASKED QUESTIONS ABOUT THE TDS VALUE
Naturally, a number of questions arise when it comes to the cleanliness, safety and health of our drinking water. Therefore, the most frequently asked questions are answered below.
WHAT IS MEASURED WITH A TDS DEVICE?
The TDS value is used to determine the amount of dissolved solids in a water sample. It thus indicates the total amount of dissolved solids in the water. This measurement is performed with a device that measures the electrical conductivity of the water. Especially salts, minerals and metals are electrically charged. The amount of dissolved particles is expressed in ppm (parts per million) or other units.
WHAT DOES THE MICROSIEMENS WATER TABLE STAND FOR?
A TDS or ppm value is calculated by measuring the conductivity of the water. TDS meters usually give a ppm value directly, which is sufficient for most consumers. However, experts and analysts prefer to use the correct value, which is given in microsiemens.
HOW HIGH OR LOW CAN THE TDS VALUE BE?
A mineral water from the supermarket has an average of 500 to 800 ppm. This is due to the minerals contained in the water. Tap water should show a similar value. Water that contains 0 ppm also has virtually no minerals, but this is harmful to the human body. Therefore, 0 ppm should not be the target.
IS IT USEFUL TO MEASURE WATER QUALITY WITH TDS AND PPM?
Only dissolved solids are considered in the calculation of TDS and ppm values, so other pollutants such as pesticides, hormones or drug residues are disregarded. Therefore, it is impossible to determine the water quality only on the basis of a ppm table. A holistic water analysis is the better alternative.
WHAT IS THE RELATIONSHIP BETWEEN THE TDS VALUE AND TASTE?
The truth is that minerals such as sodium, calcium and magnesium give water a unique taste depending on the amount present. Therefore, most people do not like the taste of demineralized water with very little ppm.
THE CONCLUSION – ON THE SAFE SIDE WITH A WATER FILTER
The Federal Office of Consumer Protection and Food Safety guarantees that tap water in Germany does not contain pathogens or contaminants in quantities that endanger health.
However, the quality of drinking water is monitored only up to the connection in the house. After that, it is the homeowner’s responsibility to provide clean and safe drinking water. Of course, there is concern here and there that copper or lead from the pipes is getting into the drinking water.
Anyone who is concerned about this can have a water analysis carried out at the responsible waterworks or at an independent institution, because the TDS value does not provide any information about how safe the drinking water is, but only that there are such things as minerals, salts and metals in the water. What these are remains unclear in this measurement.
Bottled mineral water also has traces of agricultural, industrial and domestic wastewater. In a test by Stiftung Warentest, for example, sweeteners, corrosion inhibitors and pesticide degradation products were also detected in the water.
Acetaldehyde has also been found in PET plastic bottles, which dissolves from the plastic during prolonged storage and at higher temperatures. Thus, mineral water is not necessarily healthier than tap water.
Therefore, to ensure that the drinking water from the tap is safe, water filters can help. They not only filter out pollutants from industry, pharmaceuticals and society, but also improve the taste of water. This is influenced by the composition of various minerals.