Comprehensive Guide to Factors and Solutions for High TDS Values ​​in RO Reverse Osmosis Water Purifiers

This article details the factors contributing to excessively high TDS values in RO reverse osmosis water purifiers and provides specific methods to prevent such values from exceeding acceptable limits during measurement and use.

Generally, higher conductivity and salinity result in higher TDS. A higher TDS value indicates more impurities in the water. High TDS levels suggest a high concentration of impurities, resulting in lower-quality purified water that fails to meet project requirements.

First, let's introduce the TDS measurement method:

TDS Pen Usage: Open the TDS pen probe cap, press the ON/OFF button, and after the LCD screen displays the reading, insert the TDS pen into the water being tested. Once the value stabilizes, press the HOLD button, remove the TDS pen, and read the value. After testing, wipe the TDS pen probe clean with a dry paper towel.

Factors affecting TDS value testing:

Water temperature: TDS meters cannot be used to measure high-temperature water (e.g., boiling water).

Water flow rate: TDS meters cannot be used to measure water with significant agitation.

Water pollution: TDS meters cannot be used to measure water with high pollution concentrations.

By paying attention to the above conditions, the accuracy of the test can be guaranteed, preventing measurement errors that could lead to excessively high or low TDS values.

General industry practice and national regulations stipulate that the TDS of RO reverse osmosis water should be ≤50. However, in reality, even with an RO membrane installed, TDS levels can still be high. Below are two main reasons for this:

1) During the initial water flow to the RO membrane, there is a wetting process. During this time, a small amount of residual substances from the membrane material production will dissolve in the water and be flushed out. If a wet membrane is used, the preservatives inside the membrane will also dissolve in the water and be flushed out. This process usually takes 1-2 hours, and externally, the TDS of the pure water gradually decreases. 2) A small amount of carbon powder and inorganic minerals in the post-activated carbon filter will be flushed out during the initial water flow, causing a higher TDS. The solution is to fill the pressure tank with water during the first water production, then repeatedly turn the pure water tap on and off several times to allow the pure water to flush out impurities from the activated carbon filter. This process takes about one hour.

So, what to do if the TDS value is too high? In my country, especially in northern regions, water TDS values are generally high. National municipal tap water is generally around 250, while in some areas, tap water and river/lake water have TDS values as high as 500-600, and some groundwater can reach over 1000. If the source water TDS value is too high, it is recommended to add a pre-filter before using an RO water purifier for protection.

Meanwhile, regarding the issue of the TDS value of the RO reverse osmosis water purifier not decreasing, the following aspects also need to be checked:

1) First, check the TDS value of the raw water. Generally, the R/O membrane desalination rate is 90%;

2) If it is a newly replaced reverse osmosis membrane, run it for 20 minutes before measuring;

3) Confirm whether the purified water in the storage tank has been stored for too long;

4) If the post-activated carbon filter has been newly replaced, it also needs to be flushed;

5) When measuring the purified water quality, please measure from the purified water outlet of the reverse osmosis membrane;

6) After ruling out the above causes, check if the RO reverse osmosis membrane has expired, and finally consider replacing the RO reverse osmosis membrane.