Even in big cities like Beijing and Shanghai, water from the tap may carry hazardous impurities like sediments, rusts, bacteria, viruses, chlorine, or heavy metals. Even though Chinese standards on water are equivalent to international standards, it is still not possible to ensure the safety of water due to the widespread heavy use of chemicals by industry and agriculture.
Even though water coming out from the water plant can meet the required standards, slight pollution usually occurs during the pipe delivery, due to the bad condition of some pipes in certain areas. That is why it is always good to know what is flowing from your own tap. At Greenwave we commonly used TDS testing, which is a very simple technique to quickly asses the quality of water that our clients are using.
TDS meter is portable and readily available testing kit commonly used by Greenwave and many other industry people to check the purity AND SAFETY of the drinking water. It can provide vital information to our consultants. In the content below we will explain what information can be provided by the TDS test and how to reduce the TDS reading. You will also learn about the limitations of the test.
Picture shows the TDS pen that Greenwave uses for testing. Here comparison of TDS reading between tap and purified water at the same household.
What is TDS?
This indicator measures Total Dissolved Solids and represents total concentration of dissolved substances in water that are smaller than 2 microns. TDS can be both organic and inorganic materials that are dissolved in water such as calcium, magnesium, sodium and potassium ions and carbonate, chloride, sulfate and nitrate anions.
TDS can come from different sources such as minerals in chemicals used in water treatment, chemical fertilizers from the farms etc.
A high level of TDS in water can lead to a number of health problems. The presence of potassium, sodium, chlorides increases the TDS level in the water without really posing a threat to human safety. However, the presence of toxic ions such as lead, nitrate, cadmium, and arsenic present in water can lead to a number of serious health problem. This is especially important for children because they are much more sensitive to contaminants because their defense systems are not fully developed yet.
Chlorine could be tested as well simply
Facts about TDS test
TDS test can not tell us what exactly is in the water- if the high reading is caused by toxic pollutants or simply by the Calcium and Magnesium ions that cause hardness of water. TDS simply tells us what is in water besides the pure H2O. Chlorine can not be detected by the TDS test because it is not a dissolved solid.
TDS test is still helpful
So, TDS shows both good and bad particles, is it helpful? Cities like Beijing and Shanghai source their tap water from mixed sources and use both surface and ground water. Some of the dissolved solids that are detected by TDS test can be actually good minerals. When the water goes through the mineral rocks, it collects some of the minerals present in the geological layers. That’s how we get mineral water! However, since we live in a highly industrialized country with multiple pollution issues, are a lot of chemicals and toxic particles can be found in air, soil and water. In 2012, the Ministry of Land and Resources released report which stated that 45% of ground water from 4,727 testing sites in 200 cities across China was graded as excellent, good or fair, while 55% was poor or very poor. And despite efforts to clean up the water resources, it takes many years to totally reverse the bad effects.
Therefore, it is highly likely that some of the harmful particles can be in the water around us which might not have been caught at the earlier stages of municipal purification system. Current standards for municipal water require mandatory checking of 106 testing subjects (which is compliant with international standards). But how many toxic substances are there in the whole China? (But we will tell you more about municipal water filtration in another article, stay tuned!) The most essential method to solve the tap water crisis is cleaning water resources. However, at the current stage, the most practical choice for providing clean water is using the best water filtration technology possible.
Low TDS means pureness
But we have the simple rule which says: “the higher the reading, the further your water is from the pure H2O.”Greenwave has been monitoring the TDS readings in Shanghai tap water for over 10 years and the tap water within the city had been improving gradually. You can see our measurements over the years on the below chart. The TDS reading of tap water in Shanghai dropped significantly these years with the upgrade of treatment facilities and change of water source from Huangpu river to Qingcaosha reservoir along Yangtze River.
As for Beijing, the water resources consist primarily of ground water(mineralized) surface water (for example Miyun reservoir), and Yangtze riverwater (delivered to Beijing via South-to-North Water Diversion Project).
Based on Beijing Water Resources Bulletin 2019  依据《北京市水资源公报2019》
TDS numbers could vary due to different district or the age of the apartment buildings, and condition of the piping system. As for now, the average of TDS number in Beijing is oscillating between 140 and 300 for a newly built apartment compound, but we also had clients with readings as high as 600! When we see a high TDS reading in the city, we know that part of it is probably the hard water (Mg and Ca ions are detected by the TDS) but there are certainly other things in the water, and we cannot say without more detailed lab testing.
Performance of the water filters
When buying/using a water filter, we recommend looking at the micron measurement that the filter is designed to catch if it’s available. A micron =one millonth of a meter (1000 microns=1mm).
Theoretically water filters with component of RO membrene will remove the most dissolved solids. These using activated carbon, ultrafiltration membrene or other components could not remove all. That is part of reason they are often claimed/advertised to keep the minerals. Please check the following picture for details.
Source: Water Proccessing: Third Edition’, Wes McGowan, Water Quality Association, 2001
Why some filters do not lower TDS?
Basic filters (non reverse osmosis and distillation based products) such as whole house filtration system, water softeners, shower filters, faucet filters and so on could not lower TDS reading of the filtered water dramatically. These systems mainly target at the impurities like rust, sands, chlorine and many other chemicals in the water, which means the smaller ones like metals and other charged particles can easily escape. That is to say, no matter how many stages of filters are used inside, the filtered water will be with almost no change for the reading of TDS. These basic filters can even increase the TDS reading after being used for some time, which does not necessarily mean that they are not working though.
If you are using some filter, one way to simply tell if it can lower the TDS could be checking out the materials. The following is some basic effectiveness for the materials often used in the filters.
Activated carbon: is effective at removing chlorine, pesticides, sediments, TVOCs, and improving the taste of your water, it doesn’t remove minerals, salts, or compounds that are already dissolved. (dissolved solids and very small particles don’t get removed)
KDF: (Kinetic Degradation Fluxion) process media, high-purity copper-zinc alloy that reduce contaminants and chlorine using anoxidation/reduction (redox) reaction. The zinc and copper ions are released from the KDF during chlorine removal and they are detected by the TDS test.
Spun fiber: among the most basic material removing big-sized particles such as rust, sands, sediments, but the smaller ones like metals and other charged particles can easily go through. Please remember that TDS shows only particles in water that are smaller than 2 microns, so some of the bigger particles blocked by the Spun fiber are even too big to be detected by the TDS testing.
Resin: exchanging the mineral ions out which are causing hardness in water for sodium. TDS will be hardly changed within the process.
Tourmaline: mineral stone that can add minerals, activate and alkalize the water. Such water has better taste and applied to the skin gives an excellent effect of moisturizing and absorption. We use it for our Alatai drinking water purifier. However, re-mineralizing means adding GOOD particles to the water thus increasing the TDS reading to some extent.
Ultrafiltration membrene- removing particles smaller to 0.01 um. However, for the super metal ions, they will still escape through. Thus, it will not change the TDS reading.
Reverse osmosis membrene- removing particles smaller to 0.0001 um. Only water molecules could go through theoretically. This is what we used in our Alatai, Betta and Clavo drinking water purifiers. Water through will be much lower for the TDS reading. ( less than 50 depending on the source water quality in China.) Users will notice the dramatic improvement toward taste and the purity of water.
Tips for doing the TDS test
· Temperature. Temperature will affect the testing results as it will affect the moving speed of the ions in the water. When doing a test, it's better to collect cold water or samples at least with same temperature.
· Time. Before collecting a sample, to make sure the sample is representative, it‘s better to let the tap run a while ( for example 30 seconds).
· Quantity. In terms of the quantity of water sample, half of a cup will be enough.
TDS reading for the Alatai drinking water purifier
Extra notes about TDS
· TDS test is good to help tell if the bottled water (except for the natural mineral water ) is clean and if the reverse osmosis drinking water purifiers work properly.
· If your purified bottled water (not mineral, just pure H2O) and the water TDS reading is above 50, it means the water might be fake, expired or polluted. You shouldn’t be drinking this water. However, if it is natural mineral water, it is totally normal to show high TDS reading-minerals are dissolved solids.
· TDS test is very basic. Lab tests will be still needed if you want to know what pollutants are in your water and what is their quantity.
AndyPitt Water Quality Management of Beijingin China Tsinghua science andtechnology ISSN 1007-0214 11/17 pp298-305 volume 5, number 3,September 2000i
 Beijing WaterResources Bulletin (2019)
 What’s coming out of China’s taps? https://chinadialogue.net/en/cities/4962-what-s-coming-out-of-china-s-taps/