Yesterday I had a small talk with my mother, and my mother said that it was good to have a water purifier installed at home. I tested the value with the TDS pen I bought, and it was not even 5, which was the same as what the shopping guide said at the time, and it was really good for water quality filtration. When I heard this, I immediately knew that my mother was being "**" again. I believe that many friends who are ready to buy a water purifier or buy a water purifier must have seen the merchant do such a test for everyone. Most of them will start with a glass of tap waterThen use a TDS pen to measure the value, this value is generally a few hundred larger. Then I will take a cup of water purifier to filter the water, and then test it with a TDS pen, and this value will immediately become below 10. At this time, the merchant will say:You see, if the TDS value decreases, it means that the tap water is purified and the water quality is better。The implication is to come and buy my water purifier! 
So why is it that the water quality is better when you use a thing called a TDS pen, but you can't use other pens? Here let's first explain what a TDS pen is. The TDS pen is also calledA simple portable water quality testing toolIt is a simple portable water quality testing tool used to test the TDS value of water or the conductivity of water to determine the purity or pollution of water. Many businesses that sell water purifiers will use a TDS pen to measure the water quality, and judge the quality of the water according to the value of TDS. Generally speaking, the lower the TDS value, the better the water quality, which means that the water purifier is better. There is nothing wrong with looking at it this way, but if you look closely, it is still a little kitten greasy. Because the TDS pen is mainly used to measure two indicatorsOne is total dissolved solids, which is the total amount of solids dissolved in water
In layman's terms, it is how much calcium, magnesium, lead, copper, etc. are in water. The secondIt is to measure the conductivity of water。Conductance reflects how much salt is in the water, the purer the water, the less salt it has, the greater the resistance, and the smaller the conductance. To put it simply, the lower the TDS value of the water, the less salt content in the water, the purer it is, and the better the taste. However, just testing whether there is calcium, magnesium, lead, copper, and salt content in the water really shows whether the water quality is good or bad? To be honest, it's still a bit arbitrary. Because there are 106 kinds of indicators stipulated by the state, the achievement of a single TDS indicator does not mean that the overall target is met. For example, the total number of colonies, heat-resistant coliforms, and heavy metal ion concentrations in the water cannot be measured with a TDS pen, so there is no way to say that the water quality of the water with a low TDS value is good. However, the TDS pen is not useless and can still be used as a preliminary evaluation criterion. 
After all, it is simple to operate, and it is not expensive, only a few dozen yuan, and it is very convenient to measure the water quality at home. I also have a bottom in my heart. Just like a thermometer, we can quickly use it to measure the level of body temperature when we are sick, but the thermometer cannot tell you whether you have a virus or a cold. However, we will go to the hospital when we know that the temperature is high, and similarly, if the TDS value at home is very high, we should be careful and pay attention. It shows that there is more calcium, magnesium, lead, and copper in the water, and it is better to consider buying cleaner water to drink.