How to Solve the High TDS Value (Salt Content) of Raw Water

The effluent of pure RO reverse osmosis system with a TDS 50 is typically not just direct drinking water, but also raw drinking water. Although the installation of RO reverses osmosis equipment, the TDS value remains elevated, and it is assumed that there is an issue with the device’s quality.

In general, the greater the conductivity, the higher the salt concentration, and the higher the TDS. The greater the TDS value, the higher the concentration of contaminants in water. If the TDS is too high, it indicates that there is a substantial percentage of pollutants in the water and that the quality of pure water is low, which is unsuitable for the project’s needs.

I. TDS Measurement Method

Figure 1 TDS Measurement Method

Generally, end customers or dealers are used to testing TDS directly from the tap, and this method may lead to errors. The correct measurement method is to disconnect the pressure barrel from the rear, let the machine maintain the normal water production state for about 10 minutes (the water release time of the newly installed machine should be extended by about an hour), and take water from the pure water outlet of the reverse osmosis membrane shell detection. TDS testing pen has become one of our commonly used water quality testing tools. 

Open the probe cover of the TDS pen, press the button labeled ON/OFF, insert the TDS pen into the water to be tested after the LCD screen displays, and press the button labeled HOLD after the value is stable, then take out the TDS pen to read the value. Yes, after testing, wipe the TDS pen probe clean with dry paper.

The TDS value of pure water reverse osmosis equipment reflects the content of dissolved substances in water, and the lower the value the less the content of dissolved substances in water. TDS is measured in milligrams per liter (mg/l) which indicates how many grams of dissolved solids are in 1 liter of water. These include soluble salts such as calcium ions, magnesium ions, etc.; ionic organic substances such as ammonium acetate, sodium sulfate, etc.; some heavy metal ions such as chromium, zinc, lead, copper, etc.

II. Reasons that Affect the High TDS Value

1. There is an infiltration process when the RO membrane is passed through water for the first time. During this period, a small number of residual substances in the production of membrane materials will be dissolved in water and washed out. If a wet membrane is used, the preservative inside the membrane will also be dissolved in water and washed out. This process generally takes 1-2 hours, and the external performance is that the TDS of pure water is gradually decreasing.

2. A small amount of carbon powder and inorganic minerals in the rear activated carbon will be washed out when the water is passed through for the first time, resulting in high TDS. The solution is to fill the pressure tank with water first, and then turn on and off the pure water tap several times. Let the pure water wash away the impurities in the activated carbon filter. This process takes about 1 hour.

3. The TDS value of water quality is generally high. The national municipal tap water is generally around 250, while the TDS value of tap water and river and lake water in some areas is as high as five or six hundred, and some groundwater reaches thousands. And if the TDS value of the source water quality is too high, it is recommended to add a pre-protection before using the RO pure water equipment.

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

(1) First check the TDS value of the raw water, the general desalination rate of the RO membrane is 90%;

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

(3) Confirm whether the storage time of pure water in the storage tank is too long;

(4) If the rear activated carbon is newly replaced, it also needs to be flushed;

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

(6) After eliminating the above reasons, you can consider replacing the RO reverse osmosis membrane.

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