Solutions for High TDS Values in RO Reverse Osmosis Pure Water Equipment

Generally, if the TDS of the water produced by a reverse osmosis (RO) pure water device is ≤50, it is considered potable and can be drunk directly. However, even with an RO device installed, if the TDS value is still high, the quality of the RO pure water device may be suspected. Generally, the higher the conductivity, the higher the salt content, and the higher the TDS. A higher TDS value indicates more impurities in the water. If the TDS is high, it means the water contains more impurities and the quality of the pure water is low, failing to meet project requirements.

I. TDS Measurement Methods:

Generally, end customers or distributors are accustomed to directly testing the TDS from the faucet, which may lead to errors. The correct measurement method is: disconnect the pressure tank and post-filter, let the machine maintain normal water production for about 10 minutes (new machines should extend the water discharge time to about one hour), and then take water samples from the pure water outlet of the reverse osmosis membrane shell for testing. The TDS pen has become one of our commonly used water quality testing tools. Open the TDS pen probe cover, press the ON/OFF button, wait for the LCD screen to display, insert the TDS pen into the water to be tested, wait for the value to stabilize, press the HOLD button, take out the TDS pen to read the value, and after testing, wipe the TDS pen probe clean with dry paper.

The TDS value of a pure water reverse osmosis device reflects the amount of dissolved substances in the water; the lower the value, the less the dissolved substances. The TDS unit is milligrams per liter (mg/l), indicating how many grams of dissolved solids are contained in 1 liter of water. This includes soluble salts, calcium ions, magnesium ions, etc.; ionic organic matter such as ammonium acetate and sodium sulfate; and some heavy metal ions such as chromium, zinc, lead, and copper.

II. Reasons for High TDS Values:

1. When the RO membrane is initially flushed, there is a wetting process. During this period, 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 generally takes 1-2 hours, and the external manifestation is a gradual decrease in the TDS of the pure water.

2. A small amount of carbon powder and inorganic minerals in the post-activated carbon will be flushed out during the initial water flushing, causing a high TDS. The solution is to first fill the pressure tank with water during the first water production, and then repeatedly turn the pure water faucet on and off several times to flush out the impurities in the activated carbon filter. This process takes about 1 hour.

III. Solutions for High TDS Values

In China, especially in northern regions, the TDS value of water is generally high. The TDS of municipal tap water is generally around 250, while in some areas, the TDS of tap water and river water is as high as 500 or 600, and some groundwater even reaches over 1000. If the source water TDS is too high, it is recommended to add a pre-filter before using the RO pure water equipment.

At the same time, for the problem of the TDS value of the RO reverse osmosis pure water equipment not decreasing, the following aspects also need to be checked:

(1) First check the source water TDS value. Generally, the desalination rate of the RO membrane is 90%;

(2) If a new reverse osmosis membrane is replaced, it needs to run for 20 minutes before measurement;

(3) Confirm whether the pure water in the water tank has been stored for too long;

(4) If a new post-activated carbon is replaced, it also needs to be rinsed;

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

(6) After excluding the above reasons, consider replacing the RO reverse osmosis membrane.