All You Need To Know About TDS Controller / Modulator in a Water purifier

Before buying an RO water purifier, you might have done some research about the functions of the system. During that, you must have come to know that some RO purifiers come with an extra feature called ‘TDS Controller’.

An also interesting thing you might notice that this same feature is sometimes marketed as a ‘TDS Modulator’ by some water purifier brands. However, TDS Controller and TDS Modulator are the same things and there is no functional difference between the two.

What is the TDS controller or modular?

A TDS controller helps you to control the TDS of the water.

The TDS controller is basically a valve in the water purifier that mixes two kinds of water like the water purified by a RO purification and the water without RO purification.

Now you might be surprised to know that if it is a RO water purifier then why all the water is not purified with RO purification? Because it is essential not to purify all the water with RO purification to maintain proper TDS of the water.

Safe & recommended level of TDS in drinking water 

TDS controller provides you that the level of total dissolved salts in your water is maintained.  Higher than recommended TDS level drinking water in India like 500 and above is bad for health especially very harmful for your kidneys.

The level of TDS in drinking water recommended by WHO should be between 100 and 500. Water below 100 TDS level has the tendency to dissolve even the material in its which it is kept.

On the other hand, it reacts with plastic very quickly. If the water in your area is under the recommended TDS level for drinking water, then you should always go for a UV+UF water purifier.

Working process 

TDS Controller is basically a manual device that comes with two water inputs, one water output, and a TDS Control screw.

Water Input 1:

 Purified water output from the RO membrane

Water Input 2:

It consists of two options

a) Purified Water from Activated Carbon Filter in case of RO+UV+TDS Controller Water Purifiers 

b) Purified Water from UF Membrane in case of RO+UF+UV+TDS Controller or RO+UF+TDS Controller Water Purifiers

Water Output: 

The mix of two water inputs in the required ratio.

TDS Control Screw: TDS Control screw basically controls the TDS value in output water as it manually adjusts the flow of water from the two water inputs.

  1. I) If TDS required to be reduced then the flow of input water from the RO membrane will be enhanced and the flow of input water from the Activated Carbon Filter or UF membrane will be reduced.
  2. II) If TDS needs to be raised up then the flow of input water from the RO membrane should be reduced and the flow of input water from the Activated Carbon Filter or UF membrane will be increased.

Simply, you have to turn the screw clockwise to reduce the TDS level or anti-clockwise to increase the TDS level.

Why you should buy a TDS controller

TDS means total dissolved solids. These dissolved solid could be essential minerals like calcium, magnesium, phosphorus, copper, iron, and also they could be harmful dissolved solids and solids, and heavy metals like mercury, arsenic, and lead also can be there.

RO water purifiers generally remove 90% of the total TDS of the water. So if the TDS of the water is 1000 PPM and it is purified by RO water purifier then the purified water will have TDS of 100 PPM but that is not the ideal TDS of the water. We know that TDS between 250 to 500 PPM is considered as good for consumption. The water having lower TDS like 100 PPM will have low PH value as well which it is not good for health and also it will not taste good as well.

So to maintain the ideal TDS of the water, some of the water has to be purified through RO purification and some of the water has to be purified with UV and UF water purification. The TDS controller is basically a valve adds enough amount of water not purified by RO purification to the water purified by RO purification to control and maintain ideal TDS of the water.

The alternative to TDS Controller 

There are now invented better technologies available in the market to add back the essential minerals removed by the RO purification.

RO purifiers with Mineralizer cartridges are a better option as compared to RO purifiers with TDS Controllers. Because in RO purifiers with Mineralizer, 100% of water can pass through the RO membrane. This removes any possible chances of harmful dissolved solids and heavy metals that accidentally enter in your drinking water.

What is Mineralizer 

Mineralizer or Mineral Cartridge adds back essential minerals like Magnesium and Calcium in the proper concentration in the water. It also helps to maintain the proper PH level and Acid-alkaline balance in the water.

The Mineralizer or Mineral Cartridge comes with several types of particles. Water passes from one end to the other and several essential minerals are added, and the acidic nature of water is reduced and balances the PH value of water.

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TDS Controller Vs Mineralizer 

It is discussed above TDS Controller is a small device to mix pure and raw water to maintain the desired TDS level in RO purified water. The water purifier with mineralizer is a totally different concept.

RO system with mineralizer basically works on the principles of electrolysis and ionization. In mineralizer, water purifier Electrolysis is performed in the ionization chamber by passing low voltage Direct current. 

  The water mineralizer uses Silver and copper that are also used to kill bacterial and algae and the purified water is refreshing with a better taste. 

So, the answer of the confusion ‘Whether to choose an RO purifier with TDS Controller or Mineralizer’ would actually depend on factors like the presence of industrial impurities and your own preferences. 


Both Mineralizer and TDS Controller features are quite good and provide excellent benefits if you use them appropriately. If the water supply consists of industrial impurities like lead and arsenic then you should avoid buying an RO purifier with TDS Controller. Apart from that, RO purifiers with TDS Controller can work very well in most scenarios.

On the other hand RO purifiers with Mineralizer feature can be used for water infected with lead and arsenic but these purifiers have no option to adjust the TDS level as per your requirement.

Frequently Asked Questions about TDS Controller

Is the TDS controller safe?

A high level of TDS in water can lead to a number of health problems. So you have to choose that come with a TDS controller to ensure that the water you drink is completely safe for consumption

What is TDS drinking water?

Total Dissolved Solids (TDS) is measured in milligrams per unit volume of water (mg/L) and also referred to as parts per million (ppm). For drinking water, the maximum concentration level measured and selected by EPA is 500 mg/L

Should I buy RO water purifier with TDS Controller?

RO membrane reduces the TDS level by 90%. The lower and higher TDS level limits can be changed if the RO membrane reduces the TDS level more or less than 90%.

You have to check the specifications of the RO membrane before deciding to buy an RO purifier with TDS Controller or without TDS Controller.

Can it be harmful a TDS Controller? 

In RO purifiers with TDS controller, 100% of the input water cannot pass through the RO membrane. Mixing RO purified water with non-RO purified water may cause of the presence of several harmful heavy metals like lead and arsenic in the purified water, as these impurities can only be removed by an RO membrane.

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