In daily water purification work, people often ask whether the water TDS is the hardness of water. Some even regard TDS as hardness directly. What's more, treat TDS as conductivity, etc. One by one. From this level of view, telling the truth, "water blindness" is really a lot!
In this case, you will come back to a "water science", with a scientific vision, professional spirit, truth-seeking and pragmatic attitude to talk about the respective concepts and differences between water TDS, conductivity and hardness.
Attention! After reading this article, if you still can't, don't say that you learned from Pang teacher~
1. TDS can reflect the water quality to a certain extent and has a positive correlation with the conductivity.
TDS is the abbreviation of English Totaldissolvedsolids. The Chinese translation is called total dissolved solids, also known as total salt content. The unit of measurement is milligrams per liter, or mg/L, which indicates 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 using this formula:
TDS = [Ca + Mg + Na + K] + [HCO3 + SO4 + Cl].
Due to the high solubility of water, the water includes calcium and magnesium ions, colloids, suspended particulate matter, proteins, viruses, bacteria, microorganisms and corpses, and even smaller heavy metal ions. We all know that there are very few dissolved solids in pure water, generally only about zero to several tens of milligrams per liter.
If water is contaminated or has dissolved into many soluble substances, the total solids content will increase with the increase of soluble substances.
Water purifier water quality TDS detection
The TDS concept is an exotic product that is widely used in water treatment in the United States and Taiwan. The TDS value measurement tool generally uses a TDS pen to measure the total amount of various organic and inorganic substances dissolved in water. The measurement principle actually reflects the TDS value indirectly by measuring the conductivity of the water. In the physical sense, the more dissolved in water, the greater the TDS value of water, the better the conductivity of water, and the greater the conductivity value. More commonly speaking: TDS value represents the content of dissolved impurities in water, the larger the TDS value, indicating that the impurity content in the water is large, and conversely, the impurity content is small.
1. Three factors affecting the TDS value test
1) Water temperature: TDS pens cannot be used to measure high temperature water bodies, such as hot water. The water temperature should be maintained at around 25 degrees Celsius. Remember that too high a temperature will increase the TDS value and affect the correctness. 2) Water flow rate: TDS pens cannot be used to measure water bodies with large sloshing. 3) Water pollution: TDS pens cannot be used to measure water bodies with high pollution concentrations.
For example, the tap water in Beijing is about 250ppm on average. The RO reverse osmosis water purifier can purify the TDS value to below 25ppm (calculated according to the 90% membrane salt rejection rate). When the value exceeds 30ppm, you must consider replacing the RO filter membrane or professional. The personnel check to see if the filter element has to be replaced.
2, TDS pen measures the lack of water quality and blind spots
TDS pens are not omnipotent, and its blind spots are also obvious: 1) TDS can only detect conductive substances in water, but can not detect microbial pollutants such as bacteria and viruses; 2) ions in water are not all harmful. Therefore, it is not only a TDS value to judge the quality of water, it is only a reference value; 3) It is not the most correct way to rely solely on the TDS water quality test to determine whether water quality can be eaten. Some contaminants need to be measured by more sophisticated instruments.
Of course, the TDS value displayed by the TDS pen or other similar instruments refers to the conductivity, which represents the meaning of TDS, which indirectly reflects the amount of dissolved solids contained in a certain water. For human consumption, it is already very The key is.
Second, can not rely entirely on conductivity to determine the level of TDS
Conductivity: The conductivity of water, the reciprocal of the resistance of water, is usually used to indicate the purity of water. The higher the conductivity, the stronger the conductivity, and vice versa.
Water purifier and water quality conductivity detection
It is only possible to estimate the level of conductivity by TDS. TDS refers only to the total dissolved solids in the water, ie the sum of the ions. However, the conductivity of different ions is different, so even under the same TDS, the conductivity is different due to the different ionic composition of the water.
There is an empirical formula that TDS is equal to the conductivity multiplied by 0.5-0.7.
Third, the hardness refers only to the content of calcium and magnesium ions, and the hard water is more harmful to the society of life and production.
The hardness of water refers to the concentration of calcium and magnesium ions in water. The hardness is in ppm, and 1 ppm represents 1 mg/L of calcium carbonate in water, that is, mg/L.
Everyone will look forward to the first part to understand that the hardness of water and the TDS of water are completely two concepts. It cannot be confused. The former hardness refers only to the concentration of calcium and magnesium ions in water, while the latter TDS refers to The total amount of soluble solids in water, including organic and inorganic substances, is rich in content!
1. Soft and hard water, and the concept of temporary hard water and permanent hard water
Water hardness test and comparison water purifier
Water is divided into soft water and hard water. Any water that does not contain or contain a small amount of calcium or magnesium ions is called soft water, and vice versa.
The hardness component of water, if composed of sodium bicarbonate or magnesium bicarbonate, is temporary hard water. Since this water is boiled and decomposed by sodium hydrogencarbonate, the resulting insoluble carbonate precipitates, and the water changes from hard water to soft water. If it is caused by calcium or magnesium containing sulfate or chloride, it is permanent hard water, and heating does not precipitate.
2, the hardness of water is divided into 4 levels
1) Soft water: 0-60 ppm; 2) slightly hard water: 60-120 ppm; 3) hard water: 120-180 ppm; 4) extremely hard water: 181 ppm or more.
In natural water, away from the city's unpolluted rain and snow, soft water; spring water, stream water, river water, reservoir water, mostly temporary hard water, most of the groundwater is high hardness water.
3. Three major hazards of hard water to production and life
The first major hazard: insoluble precipitates when reacting with soap, reducing the washing effect. Therefore, many brands use soap to soften the water through the soft water machine and wash the hands directly with hard water to compare the difference between the two, the washing effect is different.
The second major hazard: In industry, the precipitation of calcium salt and magnesium salt will cause scale, hinder heat transfer, and in serious cases, the boiler will explode. Due to the hard water problem, the industry will cost tens of millions of yuan each year for the repair and replacement of equipment and pipelines.
Scale and hard water are harmful to the damage of household goods and electrical equipment.
The third major hazard: drinking hard water will also have a certain impact on human health and daily life. People who do not drink hard water occasionally drink hard water, which can cause gastrointestinal dysfunction, the so-called "water and soil dissatisfaction"; cooking fish and vegetables with hard water will destroy or reduce the nutritional value of food because it is not easy to cook; use hard water to make tea Changing the color and aroma of tea reduces its drinking value; making tofu with hard water not only reduces the yield but also affects the nutrients of the tofu.
4, there will be 11 major hazards after hard water heating
Hard water will precipitate calcium carbonate and magnesium carbonate under heating. Since calcium carbonate and magnesium carbonate are insoluble in water, the impact on healthy life is as follows:
1) The mirror surface is covered with water stains; 2) The cotton clothes or towel knots are stiff and not fluffy, and the color is dim after repeated washing; 3) The water heater, humidifier and other equipment are blocked, the flow is reduced, and the life is shortened; 4) White The equipment such as bathtub or toilet is yellowed; 5) the faucet and shower nozzle are full of scale, bacteria and chrome-plated surface stains; 6) the skin is dry, rough and itchy after bathing; 7) the hair is dry and knotted. It is not easy to comb, only special shampoo can be used; 8) the water is yellow and has rust; 9) the scale is formed, which hinders the heat transfer of the heater. When the scale is too thick, the boiler will be overheated locally, causing the boiler to rupture. Accidents sometimes cause boiler explosions; 10) the unpleasant smell of disinfectant water; 11) the color of the ice produced is turbid, there is no crystal clear feeling, and the taste is also poor.
Reverse osmosis water purifier softening water quality and instant pipeline machine combination diagram
Well, there are so many sciences, and finally the key points on the blackboard, summed up: the right medicine, if you add the domestic water TDS is relatively high, the water hardness is also relatively high, the scientific solution, installed in the domestic water end with resin ions The soft water machine with exchange function softens the calcium and magnesium ions in the water. Most necessary, the RO reverse osmosis water purifier is installed at the drinking water and cooking end to thoroughly descale and purify the water (including colloid, sediment, Bacteria, heavy metals and other pollution hazards), in exchange for safe water.
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