Xiaomi Mi TDS Pen Water Quality Tester

Xiaomi is a well-known electronics company based in China. They make smartphones, laptops and other electronic devices like the MI Air Purifier 2 which I reviewed earlier. The Mi TDS Pen Tester is another of their products. As the name suggests, it looks a bit like a ballpoint pen though it is slightly bulkier. There is a cap at one end which protects the electrode sensors. The cap is also where you put the water that you are testing. The other end is for two replaceable button batteries. There is a small LCD screen which unfortunately isn’t backlit. So, not always that easy to read. To turn on the meter, just press the button. The reading should be zero. It will turn itself off after a few minutes or you can just press the button again.

TDS stands for ‘total dissolved solids’ which includes Soluble salts such as calcium, magnesium, etc, Ionic organic compound such as ammonium acetate, sodium, etc., and Metal ions such as chromium, zinc, lead, copper, etc. TDS is measured in PPM which stands for ‘parts per million’ or just mg/L which stands for ‘milligrams per liter’. Basically, the lower the reading, the higher the purity of your water. WHO says that any water with a reading of less than 300ppm is regarded as good to drink. Though you can drink any water up to about 1,000ppm. In theory, that is. It may contain harmful chemicals. More about that in a moment.

Lowering TDS is done through reverse osmosis (RO). A good RO filtering unit can reduce dissolved solids by more than 90%. Bottled water sold in Thailand and some home water purifiers may use RO together with ultraviolet treatment and/or ozone treatment. UV Water Purification systems remove 99.99% of bacteria and viruses. Ozone purifiers can remove 99% of all biological pathogens including Giardia and Cryptosporidium. The TDS meter pen can check for the purity of your water, but it cannot check for things such as bacteria, viruses and other harmful substances. For that, you will need a laboratory. All I wanted to do with the TDS meter pen was to see how well my water purifier was working. Was it reducing dissolved solids by at least 90%? First I tested my tap water which had a reading of 161ppm which is pretty good compared to some countries. I then tested my purified water and that was only 6ppm. So, I can presume that it is still doing a good job.

The Xiaomi Mi TDS Pen is easy to use. The meter pen comes with batteries already installed so that you can use it straight out of the box. All you have to do is put some water you want to test into a cup or the pen cap. Then press the button on the pen to turn it on making sure it says zero. Then put it into the water. You only have to wait a few seconds. Unfortunately, there is no hold button and so as soon as you take it out of the water, it quickly goes back to zero. So, putting the water into the cap is more efficient. In the photo above, the Mi TDS Pen is pictured together with the more bulkier TDS EZ which I bought a few years ago on Amazon. They are much alike, though the TDS EZ has a hold button which makes it easier to see the results. Their test readings were very similiar. Particularly for purer water. However, the large the number, say for example 200+ ppm, then the bigger the difference between them. But only by about 5ppm.

Once I had tested my tap water and filtered water, I naturally wanted to then check bottled water. Which brand has the purest water? But, before I give you the results, I need to give a warning. Natural spring water or mineral water will give a high TDS reading of say around 300ppm. Other bottled water may have some minerals added. Not just for health, but for taste too. Although my purified water having a reading of only 6ppm is very good, it is also tasteless and doesn’t contain any minerals that your body may need. But, I don’t care so much, I can easily get minerals from eating a balanced diet. So, here is the result of these popular brands of bottled water sold in Thailand. You might be surprised by some of the results: (1) Crystal 20ppm, (2) Chang 122ppm, (3) 7 Select 5ppm, (4) Singha 344ppm, (5) Nestle Pure Life 220ppm, (6) Namthip 25ppm, and (7) Avias 36ppm.