What is a TDS Controller in a Water Purifier?

If you have done some research offline or online before buying the best water purifier in India 2022 , then you must have encountered the term TDS controller. Sometimes it is also known as the TDS modulator. A water purifier, especially the Reverse Osmosis ones purify water by terminating all the impurities, including the TDS. It removes 90% of the TDS level in the water. If you have around 1500 ppm TDS water supply, then after the RO purification system, it will come around to almost 150 PPM.

But the water with 150 TDS will not have any odor or taste because of the removal of important minerals and nutrients like magnesium, calcium, and sodium. The water will have a low pH level and will thus taste bitter. A special mechanism called the TDS controller will rectify this problem anomaly. In this article, we will share what is a TDS controller, how it works, and its advantages and disadvantages.


What is a TDS Controller in a Water Purifier?


Definition of TDS Controller

TDS controller is a device that can control the TDS level of the water. Unlike the cartridges, membrane, and filter, the TDS controller does not purify the water further. The RO process reduces water hardness by almost 90%. It is a screw oriented small device that keeps the salt level in the water in control. It operates through a bypass valve that passes a percentage of water to the UF, carbon, or UV chamber without letting it pass through the RO membrane. The total number of sequences and the filtration method varies from product to product.


How does a TDS Controller operate?

TDS controller is a manual device that comprises two water inputs, one output for water, and a TDS controlling screw. It operates in the following way.


Water Input Type 1

This is the output for the purified water that passes through the RO membrane.


Water Input Type 2

Purified water from the activated carbon filter enters through this input in the case of RO+TDS+UV water purifiers. In the case of RO+UF+UV+TDS or RO+TDS+UF purification system, purified water from the UF membrane enters through this input.


Water Output

Through this output, you will get the mixture of the two water inputs in the ratio according to your requirement.


Screw for Controlling TDS

TDS controlling screw helps in keeping in check the TDS of the output water by a manual adjustment of the water flow and the two inputs of water. If the TDS needs to be decreased, then the input water from the RO membrane should be increased. In the case of a machine with UF or UF chambers, the input water from those filters should be reduced.

If the TDS needs to be enhanced, the input water flow from the RO membrane should be reduced, and the water input from the UF or Activated Carbon filter should be increased. In simple words, turn the TDS controller screw clockwise or anti-clockwise to decrease or increase the TDS level. In most of the water purifiers, the TDS controller is fitted inside the machine. Thus to adjust it, you have to open the outer cover first.


Benefits of a TDS Controller

Below are some of the other benefits of the TDS controller apart from making the water healthy.


TDS controller is an economical and cheap device that might cost you 50 to 100 INR. It is a one-time investment that you need not change for many more years.



A RO water purification system with a TDS controller wastes less water during the filtration procedure. This makes it more eco friendly and efficient.



Including a TDS controller in the water purifier will give you complete freedom to control the TDS level as per your will. You can also completely close the output coming from type 2 water input, and you will get 100% purified RO water.



Since TDS controllers add the required minerals to the water input source, therefore the result contains more nutrients and minerals in them.


Drawbacks of TDS Controller

The resultant water from the RO purification system with the TDS controller device may not be completely 100% pure. Since the controller mixes the water that does not pass through the RO membrane to the output source, it will include all the chemicals and minerals that were originally there in the input water in a small amount. Generally, this is not a problem unless the principal water source includes heavy toxic metals like nitrate, cadmium, arsenic, and lead. If the output water includes these metals under the safe limit, then you can consume the water from the TDS controller with no worries.


Is it Safe to Buy a RO Water Purifier with TDS Controller?

You can purchase a RO water purifier with a TDS controller if the TDS level of the raw or input water is less than 900 PPM and more than 300 PPM, It should not contain any heavy metal like arsenic and lead. If the primary water source contains heavy metals, then this device is not ideal for you.



TDS controller is perfect for enhancing the TDS count in a RO water purifier. Which one will you choose will depend on your personal choice, TDS count, and heavy metal in the water source? We would suggest both the TDS controller and RO filtration system if you have a TDS level lower than 1200 mg/litre with a small number of heavy metals.

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