What is MTDS in Water Purifier and How it Works

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In Brief: What is MTDS in Water Purifier?

MTDS or Manual TDS regulator is a small device that lets you adjust the TDS level of an RO system. In isolation, reverse osmosis tends to reduce the TDS level of water below the ideal amount. This device regulates the flow from various sources to optimize the TDS level in the output water. Though inexpensive, it cannot remove heavy metals.

When it comes to the field of water purification, there are so many abbreviations visible on the relevant platforms. RO, UV, UF, MF, NF, etc.; it can get a little confusing.

Whether it’s a service center, showroom, or online content, these terms seem to be everywhere. While there are certain common factors across each of these terms, they are all very different.

Another abbreviation often found associated with combined water purification systems is MTDS. This article explains what exactly MTDS is and why it is useful.

What is MTDS in Water Purifier and How it Works

MTDS stands for Manually Total Dissolved Salts controller.

It is a regulator present in select RO models of various water purifier brands. [1]

The purpose of this device is to adjust the TDS level in the output water from the purifier. It is not a filter or sieve.

It is an accessory meant for RO systems as these purifiers tend to remove almost all TDS from water. This can be an undesirable outcome as the ideal level for TDS is between 100 to 300 PPM.

A level below 100 PPM is not advisable as that water lacks essential minerals and salts required by the body. A level between 300 PPM and 900 PPM is still acceptable.

Check more details on TDS acceptable level here>

But TDS levels above 900 PPM are unfit for human consumption.

Having an MTDS regulator along with your home’s water purification systems gives you control over this level. It is a small device that attaches to the purification system towards the end.

The exact location depends on whether the system is just RO or a combination of RO, UF, and UV. Depending on the location, the MTDS regulator is supplied with water from two inlets.

One comes from the RO and the other comes from a different source based on what types of filtration methods are being used. When the system only uses reverse osmosis, the second input comes from the activated carbon filter.

With RO+UF, the second input comes from the UF filter. If the system also has UV, the second filter comes either from the activated carbon filter or the UF filter according to the setup.

Once water passes through the MTDS regulator, it goes through the UV filter. The logic behind these arrangements is the mechanism of the MTDS regulator.

It is a device that controls the water flow from both these inputs.

If the TDS level needs to be decreased, the RO water flow is increased. If the TDS needs to be increased, the second input water flow is increased. By doing this, the MTDS regulator balances the flows to give the optimal TDS level.

This is an effective system as the water before the RO filter is free of suspended impurities.

Therefore, it is clean except for the dissolved salts and minerals. When the system is complemented with a UV filter, it takes the water from the MTDS.

This input, now with the right TDS level, is treated for microorganisms present in the water.

The result is purified water with the desired amount of salts and minerals. The following diagram represents the input and output streams of the MTDS controller.

Benefits of MTDS in Water Purifier

By optimizing the TDS level of drinking water, the MTDS regulator provides the human body with the required salts and minerals.

The retained dissolved solids help improve the pH of the water according to bodily needs.

This also improves the taste of the water. Ordinary RO water tends to have a flat taste. The right TDS level lets water taste like it is meant to.

The MTDS controller also prevents the TDS from being too high, which produces a brackish taste. Since it can be manually adjusted, the taste can be changed to suit the unique needs of homeowners.

The biggest advantage of a device like the MTDS regulator is that it is highly inexpensive.

At just a nominal price, it can adjust the TDS of water, virtually undoing one of the cons of reverse osmosis.

Limitations of MTDS in Water Purifier

MTDS regulators have a very simple operating mechanism, which is cheap and convenient. However, this mechanism does not remove heavy metals from the water.

As two streams are going into the controller, and one of them comes from pre-RO treatment, the metals remain. So, this is not an appropriate device if the supply water contains substances like lead, copper, or arsenic.

Another disadvantage to an MTDS regulator is that it is rather hard to access. Some purification systems require the removal of a side panel to reach the MTDS controller.

However, other models have it in a more accessible location.

Depending on the style of the MTDS regulator, it can be adjusted by hand or by a screwdriver. Sometimes, it’s a little tricky to adjust the TDS level and it may take repeated trials to get it right.

When to use MTDS in Water Purifier

An MTDS regulator should be used if the supply water comes from separate sources. Even if these different sources have varying levels of TDS, this controller can adjust them to suitable levels.

If you are using an RO in the first place, it means the TDS level of the supply water isn’t safe. But the RO reduces this level to below 100 and that’s why an MTDS controller is useful.

However, one should get their supply water tested in a laboratory to check for heavy metals.

If the water contains substances like lead, mercury, or arsenic, an MTDS regulator is not enough. In that case, an additional mineral cartridge is a better option.


An MTDS regulator is a manually adjustable device that controls the TDS level of an RO system’s output water. It is fed water from the RO filter and a filter stage right before the reverse osmosis stage.

The MTDS device regulates the flow rates of various sources of water to either increase or decreases the TDS level. This controller is quite cheap and can be set by hand or by a screwdriver.

Having a regulator like this in a water purification system improves the taste and pH of water.

It gives out the right amount of salts and minerals in drinking water. However, this device is not good enough if the supply water contains heavy metals.