Everything You Need to Know About TDS Controller/ Modulator in a Water Purifier

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You have come across the term TDS Controller. However, you might not know what it is. It  is basically used in a RO water purifier.

 The article below educates you regarding this aforesaid term in detail. Therefore, continue reading to understand the term better.

What is a TDS Controller?

From the name, it is evident, a TDS controller is a device that controls the TDS level of the water. Note that unlike cartridges and membranes, TDS controllers neither purify nor filter the water.

It basically acts like a valve in the water purifier mixing the purified water ( by RO purifier) and the non-RO purified water.

It is done just to maintain the TDS level in the water.

How Does it Work?

The device comes with 2 water inputs, one water output and a TDS control screw.

TDS working

1st Water Input: Purified water output (from the RO membrane).

2nd Water Output: It comes with 2 options.

  • RO+UV+TDS Controller water purifiers – Purified water from Activated Carbon Filter.
  • RO+UF+UV+TDS or RO+UF+TDS  Controller water purifiers – Purified water from UF Membrane

Water Output: The mixture of 2 water inputs in a required ratio.

TDS Control Screw: It controls the TDS value in the output water, manually adjusting the flow of water from the 2 water inputs.

  • If TDS needs to be reduced then there will be an enhanced flow of input water from the Activated Carbon Filter. Otherwise, UF Membrane will be reduced.
  • Now, if TDS is needed to be raised then there will be a reduction in the flow of the input water from the RO Membrane. Thus, there will be an increased flow of input water from the ACtivated Carbon Filter or the UF Membrane.

Note that to reduce the TDS level, just turn the screw clockwise. Similarly, turn it anti-clockwise to increase the level.

The Need for TDS Controller

There are several essential minerals like calcium, magnesium in natural water. Natural water may also contain other harmful impurities like fluorides, arsenic and etc.

These minerals and heavy metals together constitute the dissolved solids. These dissolved solids in water are referred to as TDS (that is Total Dissolved Solids) levels.

Now, the presence of these minerals like calcium, magnesium in small quantities is good for drinking water. They make the drinking water healthy.

However, RO Membrane generally removes nearly 90% of dissolved solids including these minerals from the input water.

Thus, if there is a lower TDS level in the input water, then it is due to the RO Membrane. It has significantly reduced the level of essential minerals making the water unfit for drinking.

Therefore, now there is a need for this TDS Controller. In such a case, TDS Controller increases this purified water to make it healthy

Recommended TDS Level in Drinking Water

According to WHO, the recommended TDS level in drinking water is between 100-500. Below 100 TDS level, water tends to dissolve even with the material on which it is kept.

tds level

If you find the water in your area is below the recommended level, then go for a UF+UV water purifier.

The water having a higher TDS level than recommended affects your Kidney. Note that both higher and lower than the recommended level is not healthy.

TDS Controller – Recommendation

TDS Controller is not the ideal way to add minerals to the purified water. Mixing of purified and unpurified water might result in several harmful heavy metals in the purified water.

Note the following 2 points before buying an RO water purifier with TDS Controller.

  • If the TDS level of the raw water is below 900 ppm.
  • If the water does not contain heavy metals ( lead, arsenic).

Alternative to TDS Controller – Mineralizer

RO purifiers with Mineralizer Cartridges are a better alternative to the RO purifier with TDS controllers. It is because 100% of water can pass through the RO Membrane in the RO purifiers with Mineralizers.


Therefore, it easily removes harmful dissolved solids and heavy metals that have entered the drinking water.

Mineralizers add back a proper concentration of essential minerals. Also, it maintains a proper pH and Alkaline level in water.

TDS Controller vs Mineralizer

TDS Controller Mineralizer
100% input water does not pass through RO Membrane. 100% input water passes (is purified) through RO Membrane.
It is not ideal for water having higher concentration of harmful heavy metals like lead, arsenic. The harmful metals are removed as 100% water passes through RO purification.
You can adjust ( increase or decrease) the TDS level of the purified water. You cannot adjust the TDS level of the purified water.
Cheaper and smaller in size. It is as big as a regular filter or cartridge in a RO purifier. The price is slightly higher than the TDS controller (above 500).

Final Thought

In short, we can say that between choosing a TDS controller or Mineralizer, it depends on the water. If there is a higher concentration of industrial impurities, then using Mineralizer is better.

However, the choice is yours. Check the comparison table and choose accordingly.


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