What is TDS meter and how TDS meter works?

TDS meter

TDS meter is small digital device which measures presence of total dissolved solids in water. When TDS meter is brought in contact with water it displays TDS reading on device.

TDS meters display the TDS value in parts per million (ppm). 1 ppm indicates 1 milligram of dissolved solids per kilogram of water.

1. What is TDS?

Water that we have in our surrounding are from different sources like surface water, ground water, municipal water etc and contains certain amount of dissolved solids. These solids which comprises of various organic or inorganic substance become integral part of water because of natural process or human activity with the time.

The most common minerals found in water are Calcium, Magnesium, and Sodium. Which get dissolved after water falls to the ground as rain and they remain in the water at various levels of concentration. Minerals presence in water helps in building water taste by slightly raising the pH of the water.

Dissolved solids presence in water is from both organic sources as well as inorganic sources. Most common sources are vegetation, silt, plankton, and industrial waste and sewage, runoff from urban areas, road salts used on street during the winter, and fertilizers and pesticides used on lawns and farms etc.

Most of these minerals and specially salt dissolves in water forming ions. Total dissolved solids(TDS) is the sum of the cations (positively charged) and anions (negatively charged) ions in the water.

TDS value from natural sources have been found to vary from less than 30 mg/litre to as much as 6000 mg/litre, depending on the solubility of minerals in different geological regions.

2. What does TDS meter not measures?

Value of TDS meter can’t be stand alone taken as measurement of purification of water. TDS is just one type of impurity in water and value to TDS meter under range does not rule our presence of other types of impurities in water.

TDS does not measure following parameters


Its can be biological or chemical. TDS does not measure presence of contaminants like pesticides, pharmaceuticals, hexavalent chromium, bacterial, E coli etc. It will also not give you measurement of the presence of harmful heavy metals like lead or phosphorous.

Health of water

There are few minerals like potassium, magnesium, and calcium which are essential for human body growth. TDS meter will show a high value for presence of these healthy minerals also even in presence of any other dissolved solids. Simply because TDS meter does not differentiate between type of mineral while calculating its reading.

3. How does TDS meter works?

TDS meter works on the fundamentals of electrical conductivity (EC) of water. Pure water (H20) has virtually zero conductivity.

The ideal way of measuring TDS is to evaporate the water first and after that weigh the solid residue. While practically, the TDS level is estimated by measuring the EC of the water with a meter and converting it to TDS value. Electrical conductivity of the water can be measured easily by passing a small current through it.

Thus a TDS meter is actually an EC meter calibrated in TDS, estimating the TDS from the EC. Some of the TDS meters displays either value.

In general conductivity is about 100 times the total cations or anions expressed as equivalents. TDS is calculated by multiplying EC by a factor of 0.5 to 1.0 times, depending upon the levels. Higher the EC level, the higher is the conversion factor(KE) to determine the TDS.

how tds calculated hozone

The conversion factor may varies with temperature and few TDS meters take this into account and adjust values accordingly.

4. What is TDS chart for drinking water?

TDS value of the meter and its significance can be understand through this tds chart which maps various TDS value to corresponding information.

TDS chart for drinking water
Tds chart

As per the Indian Govt, BIS standard and WHO standard, if TDS value of water in your home is less than 500 mg/L, it is safe to drink. Don’t get trapped by RO salesman who would bombard you with technical terms to convince you have you need water with 0-10 TDS range.

If TDS meter is indicating value less than 300 mg/L, you should avoid using RO water purifier as that is not essential and using that would remove the essential minerals. Rather you need to focus on UV or UF purifier which purifies any biological impurity.

A low TDS valued water does not means more purified water, rather it is more demineralized water.


  1. There can be slight variation of electronic TDS meter value compared to practical value through lab test.
  2. TDS meter need to be calibrated after 15-20 usage as after that it will starts giving you wrong reading. This calibration can be done with any alkaline solution.

5. How to calibrate TDS meter?

TDS meter can give you accurate reading for 10-15 times usage. After that these meter required to be calibrated for getting correct reading. Your TDS meter may require more immediate calibration if you are testing frequently water with TDS level > 1000 ppm.

TDS meter can be recalibrated using a commercial standard NaCl-based solution which is having standard ppm and a screwdriver to adjust reading.

  • Prepare NaCl-based solution, which is approximate 0.5 µS of conductivity.

  • Immerse the meter in the calibration solution.

  • If the meter reads accurately as per standard ppm value of solution or it is within 2% variation, no calibration require.

  • However if variation is more than 2% in reading then it require calibration. For that adjust the reading by inserting a mini screwdriver into the trimmer pot which is hole on the back of the meter.

6. What are Best TDS meters online in India?

There are many different types of TDS meters available for measuring TDS value of drinking water and some of them are having features to show temperature and conductivity also along with TDS value.

6.1 Generic Digital LCD TDS Meter Tester


  • The product comes with HOLD button which helps you in keeping TDS value hold on screen. Otherwise as soon as you will pull a TDS meter out from water value will disappear.

  • Built-in digital thermometer for temperature measurement. For using this you need to press the TEMP button. The display will switch to temperature.

  • This TDS meter comes with water level limit that helps you in being aware of dip level in water.

  • Easy calibration feature with TEMP and HOLD button.

6.2 HM Digital TDS Meter – best TDS meter in India


  • Measures total dissolved solids (TDS) and temperature.

  • Automatic temperature compensation (ATC) for showing accurate TDS value.

  • Water-resistant housing.

  • High TDS measurement Range from 0-5000 ppm.

6.3 IONIX Imported Tds Meter tester


  • Similar features of Generic TDS meter with HOLD and TEMP button.

  • High accuracy and precision of reading.

  • Comes in multicolour model with pH testing strip.

  • Usage removable battery

6.4 Luzon Dzire TDS3 Pocket Digital TDS Meter


  • Hold Function and a Built-in digital thermometer for temperature measurement.

  • Highly efficient and accurate due to its advanced microprocessor technology.

  • Replaceable battery and carry case.


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