With the increasing probability of water pollution, water treatment equipment is becoming increasingly important in people's minds, gradually entering people's homes, and TDS pens for water testing are also selling well online. However, water treatment equipment manufacturers have found that many users are purchasing through online sales. They are not very clear about the TDS value and are confused about questions such as "What is the TDS value of drinking water?" and "What is the normal TDS value of drinking water?" So, can the TDS value really become a key factor for customers to understand water quality and purchase water treatment equipment?

 

TDS refers to the total dissolved solids concentration in water, mainly reflecting the concentration of calcium, magnesium, and potassium ions in water and the relationship between water strength and resistivity. Its measurement principle is relatively simple, referring to the equivalent substitution method of water purity through a resistor. Since pure water is an insulator, natural water contains carbonates and organic compounds, becoming an electrolyte. The greater the impurities in the water, the greater the conductivity.

First, the TDS value does not reflect the quality of water.

China has vast territory, and the water quality in some areas is unique, and drinking water standards also vary. Drinking water from factories that meet the standards is harmless to human health; some have a TDS of over 1000, while others may be less than a few tens. Water treatment equipment manufacturers would like to remind you that TDS only measures the conductivity of water and cannot measure harmful substances such as bacteria and viruses in the water.

Secondly, the TDS value cannot accurately measure water hardness.

Water treatment equipment is generally referred to as having moderate water hardness, mainly determined by the content of calcium and magnesium ions. However, the TDS value reflects the total content of calcium, magnesium, sodium, potassium ions, carbonate ions, bicarbonate ions, chloride ions, and other ions in the water, which is significantly different.

Thirdly, TDS does not indicate water acidity or alkalinity.

Water acidity or alkalinity is determined by the pH value of the water, which is related to the concentration of hydrogen ions in the water. The TDS value is not directly proportional to the hydrogen ion concentration.

Finally, the TDS value cannot be the sole indicator of water purifier filtration quality.

The TDS value generally only reflects whether the water treatment equipment achieves the filtration effect. Conductive minerals and ions in the water can pass through, so the TDS value cannot simply represent drinking water quality and the filtration accuracy of the water purifier.

Soft Water and Water Hardness

Water with little or no calcium and magnesium ions is called soft water; otherwise, it is called hard water. If the hardness components are caused by calcium carbonate or magnesium bicarbonate, it is temporary hardness (boiling temporary hard water, dissolving calcium carbonate, and insoluble sulfide deposits, the water becomes soft water). If it is caused by calcium and magnesium sulfates or fluorides, it is permanent hardness. According to the total hardness value, total hardness is 0-30 ppm, total hardness above 60 ppm is considered hard water, and high-quality drinking water should not exceed 25 ppm; high-quality soft water has a total hardness below 10 ppm.

Relationship between Water Conductivity, Strength, and TDS?

In daily water purification work, people often ask if water TDS is water hardness? Some even directly equate it with TDS. More importantly, it is called strength TDS, looking at resistivity, etc., which varies. From this perspective, frankly speaking, there are too many "water blind" people!

In this case, let's have another "water science popularization" from a scientific perspective, a more professional spirit, and a pragmatic attitude to understand the concepts of freshwater TDS, resistivity, and strength, as well as the correlation and differences between them.

1. TDS can reflect water quality to a certain extent and has a positive correlation with resistivity.

TDS is the abbreviation of Total Dissolved Solids, which is translated into Chinese as total dissolved solids, also known as total salinity. The measurement unit is mg/liter, which means how many milligrams of total dissolved solids are dissolved in 1 liter of water, or the total amount of ions in 1 liter of water.

TDS can also be expressed by this formula:

TDS = [Ca+Mg+Na+K] + [HCO3+SO4+Cl].

Because of water supersolubility, water contains chlorites, colloids, particulate pollutants, proteins, viruses, bacteria, microorganisms, remains, and smaller metal ions. As we all know, the dissolved solids in mineral water are very low, generally only zero to a few tens of mg/L.

If the water source is polluted or various soluble chemical substances are dissolved, the total solids content will increase with the increase of soluble substances.

Water Treatment Equipment Water TDS Testing

TDS is an imported term, widely used in the Taiwan wastewater treatment industry. TDS is generally measured using a TDS pen, which can measure the total amount of various organic and inorganic compounds dissolved in water. The measurement principle is actually to indirectly reflect the TDS value by measuring the conductivity of pure water. In the physical sense, the more dissolved substances in the water, the higher the TDS value, and the better the water conductivity and the lower the resistivity. Another popular saying is: the TDS value represents the impurity content of dissolved substances in the water; the higher the TDS value, the more impurities in the water, and vice versa.

1. Three Factors Affecting TDS Value Testing

1) Water temperature: TDS pens cannot be used to measure continuously high-temperature water, such as boiling water. The water temperature should be kept around 25℃. Remember, too high a temperature will affect the accuracy. 2) Water flow rate: TDS pens cannot be used to measure water with large fluctuations. 3) Water pollution: TDS pens cannot be used to measure water with relatively high pollution concentrations.

For example, the average drinking water in Beijing is around 250 ppm. The RO reverse osmosis water purification reduces the TDS value to below 25 ppm (calculated according to the conductivity of 90% membrane water). When the value exceeds 30% ppm, consider replacing the RO filter paper or asking a professional to check whether the filter needs to be replaced.

2. Precise TDS Measurement Addresses Water Quality Issues and Blind Spots

A TDS meter is not the only solution, and its limitations and blind spots are quite obvious: 1) TDS meters only accurately measure the electrically conductive chemicals in water, not bacteria or other microbial contaminants; 2) Not all positive ions in water are harmful, so relying solely on TDS as a standard for water quality is insufficient; 3) Relying solely on TDS to determine if water is safe to drink is not the most accurate method. Some contaminants require more precise instruments for accurate measurement.

Naturally, the TDS value indicated by a TDS meter or similar instrument refers to electrical conductivity, which indirectly reflects the total dissolved solids in a certain type of water, which is also very important for human health.

2. Electrical conductivity cannot be solely used to determine the TDS value.

Conductivity: Water conductivity is the reciprocal of water resistance, generally used to indicate water purity. Higher conductivity indicates less pure water, and vice versa.

Water treatment equipment and water conductivity detectors

It can only roughly estimate the possible TDS based on conductivity. TDS only refers to the total dissolved solids in water, i.e., the sum of positive ions. However, different ions have different conductivities, so even with the same positive ions, the conductivity of TDS varies due to the different ionic compositions of the water.

There is an empirical formula, where TDS is approximately equal to conductivity multiplied by 0.5-0.7.

 

3. Hardness only refers to the chlorite content; water hardness is quite harmful to life and production in society.

Water hardness refers to the concentration of calcium and magnesium ions in water. The unit of hardness is ppm, with 1 ppm representing 1 mg/L of calcium bicarbonate in water, i.e., mg/L.

Referring back to the first section, water hardness and TDS are completely different things and should not be confused. The former refers only to the concentration of calcium and magnesium ions in water, while the latter, TDS, refers to the total amount of dissolved solids in water, including organic and inorganic compounds.

1. Soft water and hard water, and the concepts of temporary and permanent water hardness

Water hardness testing and comparison of water treatment equipment

Water with little or no calcium and magnesium ions is called soft water; the opposite is also true.

If the water hardness components consist of sodium bicarbonate or magnesium bicarbonate, it is temporary hardness. Because boiling dissolves sodium bicarbonate and insoluble sulfides precipitate, the water hardness becomes soft water. Hardness that contains calcium, magnesium, potassium thiocyanate, or fluoride is permanent hardness and does not precipitate upon heating.

2. Water hardness is divided into four levels

1) Soft water: 0-60 ppm; 2) Slightly hard water: 60-120 ppm; 3) Moderately hard water: 120-180 ppm; 4) Very hard water: above 181 ppm.

In natural water, precipitation and snow far from urban areas and free from pollution belong to soft water; mountain spring water, streams, rivers, and reservoir water often have temporary hardness and are often high-hardness water.

3. Three major harms of water hardness to equipment and life

The first harm: Reaction with soap causes insoluble precipitates, reducing cleaning efficiency. Therefore, there is a significant difference between using soap softened by a water softener and using hard water for hand washing and disinfection; the cleaning effect is different.

The second harm: In industry, the deposition of calcium, magnesium, and salts leads to scale, hindering heat transfer, and in severe cases, causing boiler explosions. Due to water hardness issues, millions of yuan are spent annually on maintenance and pipe replacement in industry.

Scale and water hardness damage to daily necessities and electrical equipment make purification crucial.

The third harm: Drinking hard water can also have certain adverse effects on health and daily life. People who don't usually drink hard water may experience gastrointestinal discomfort after drinking it, which is often referred to as "water and soil incompatibility"; cooking fish and vegetables with hard water will damage or reduce the nutritional value of the food because it is not easy to cook; using hard water to make tea can change the color and taste; using hard water to make tofu will not only reduce the yield but also affect the nutritional content of the tofu.

4. Eleven harms of heating hard water

When hard water is heated, calcium carbonate and calcium sulfate precipitate. Because calcium bicarbonate precipitates calcium carbonate and calcium sulfate, and calcium sulfate is difficult to dissolve in water, the following effects on healthy living are observed:

1) Water stains on mirrors and glass; 2) Stiff and less fluffy cotton clothes or towels, dull color after several washes; 3) Clogged drains, reduced flow rate, and shortened lifespan of electric water heaters, humidifiers, etc.; 4) Yellowing of white bathtubs or bathroom fixtures; 5) Faucets and nozzles clogged with scale, mold, and water stains on stainless steel surfaces; 6) Dry, rough, and itchy skin after showering; 7) Dry, tangled hair that is difficult to manage, requiring special shampoo; 8) Yellowish and rusty water; 9) Scale formation restricts the heat transfer of electric heaters. When the scale is too thick, it can cause overheating of the heater, leading to cracks and accidents, sometimes even causing boiler explosions; 10) Pungent smell of disinfectant; 11) Cloudy, not crystal-clear, and poor-tasting ice cubes.