Are you planning to buy a new water purifier? One word that you encounter frequently is TDS. What is TDS?

Read on to know everything about TDS. We shall also look at ways how to measure TDS. We will also discuss the acceptable levels of TDS and how to eliminate TDS from the water.

What is TDS?

TDS stands for “Total Dissolved Solids.” Our Chemistry teacher teaches us that the molecular formula for water is H2O. Therefore, every molecule of water contains two atoms of Hydrogen and one atom of Oxygen. It is true of pure water.

However, the water available on this planet contains a lot of salts like calcium, magnesium, potassium, fluorides, carbonates, and sulfates and many others. It is a long list.

Also, the groundwater and other water sources like rivers, lakes, and ponds contain heavy metal impurities like arsenic, lead, and mercury. These chemicals are dangerous. Therefore, you need appliances like water purifiers to eliminate these contaminants.

At the same time, excessive salt intake can also be harmful to health. There is a need to regulate the levels of TDS in water.

Is TDS necessary?

Ideally, you should consume pure water. However, pure water does not have any taste. Salts like calcium, magnesium, and potassium are necessary to impart the required flavour and nutrition value. However, you should ensure that you maintain the levels of TDS. Let us now see the acceptable levels of TDS.

TDS – Acceptability Levels

The Bureau of Indian Standards (BIS) decides the acceptability levels of TDS in water. According to BIS, the TDS up to 500 mg/litre is acceptable. The following table can make things clear.

TDS Levels mg/litreReasons for Acceptability/Non-acceptance
Less than 50This level is unacceptable because water with such a low proportion of TDS does not contain the required minerals for healthy growth.
50 to 150It is an acceptable level because there are industrial and other types of pollution involved
150 to 250This level of TDS is the healthiest as far as cardiovascular health is concerned
250 to 350There are places in India where the ground level water has TDS levels in this range. It is also an acceptable level
350 to 500The BIS certifies water with TDS levels up to 500 as acceptable for human consumption
Above 500 and up to 1200Any level over 500 is not acceptable for human consumption. However, you can purify this water using RO and other kinds of water purifiers. It can result in the elimination of excess TDS thereby reducing it to below 500 and making it fit for consumption.
Above 1200Water having TDS levels over 1200 is utterly unfit for human consumption.

TDS – Palatability Levels

There is a difference between the acceptability and palatability levels of TDS in water. We shall now look at the palatability levels of TDS before proceeding with measuring the amounts of TDS in water.

TDS Levels mg/litrePalatability Quotient
Any level less than 300Excellent for drinking
More than 300 and up to 500These levels are acceptable
500 to 900As you can eliminate the excess TDS by using water purifiers, it is a fair level.
Above 900 to 1200High-quality water purifiers can reduce TDS levels in this range as well. However, water having TDS level in this range constitutes poor palatability.
Above 1200It is an unacceptable range.

How do you measure TDS levels in water?

You can measure TDS levels in water using three methods. Let us look at them in brief.

1. Using Digital TDS Meter (Easiest)

The Digital TDS Meter is the easiest of all the methods used to determine the TDS levels in water. The most significant advantage of the Digital TDS Meter is that you do not have to take any readings and do calculations using mathematical formulas. You get immediate results. Let us look at the simple procedure for the benefit of all.

Measure the temperature of the water sample

  • Switch on the meter
  • Press the ‘TEMP’ button. You get a reading in Degrees Celsius.
  • Return to the TDS mode by pressing the ‘TEMP’ button again.
Digital TDS Meter

Measure the TDS level

  • Remove the protective cap and switch on the meter.
  • Immerse the TDS meter into the water sample up to the maximum immersion level. Usually, it is 2 inches. There is a marking on the meter to indicate this level.
  • There might be some air bubbles in the water. Gently stir the meter to remove these air bubbles.
  • Wait for about 10 to 15 seconds for the reading to stabilize.
  • Press the ‘HOLD’ button and take it out from the water for viewing the reading.
  • Some meters display the X10 symbol. Under such circumstances, you have to multiply the reading by 10.
  • After using the TDS meter, shake off the excess water from the meter and replace the protective cap.

You have to take the following precautions while using the TDS meter.

  • The Digital TDS meter is not watertight. Hence, you should ensure not to dip the meter beyond the maximum immersion level.
  • Do not expose the meter to direct sunlight.

Where can you get these digital TDS meters?

Generic Digital TDS Meter

These Digital TDS meters are available at medical stores and other retail establishments for a few hundred rupees. You can also order them online from online retail stores such as Amazon. These meters are available in various calibrations. TDS meters are having a measurement range of even 0 to 5000 ppm.

How to test reverse osmosis drinking water quality with a TDS meter – APEC Water

2. The Electrical Conductivity Meter Method

We have seen that TDS constitutes both organic and inorganic salts. The Electrical Conductivity Meter method is the most common one in use today. Follow these steps to calculate the level of TDS in water.

Apparatus required for measuring the TDS.

  • A sterilized glass beaker free of dust
  • The water sample should be around 250C
  • An electrical conductivity meter

The electrical conductivity meter works by releasing an electrical current into the water thereby measuring its resistance.

Electrical Conductivity Meter

Measure the conductivity

Ensure that you keep the beaker on a flat surface. Switch on the conductivity meter and insert the measuring lead into the water.

  • The reading will fluctuate a bit for a few seconds before stabilizing. You should note down the reading after it stabilizes.
  • This measurement is the purity of water. The reading is in µS (micro Siemens). The lower the value, the purer is the water. Water in its purest H2O form has 0 µS.

Enter the data into the following formula to arrive at the TDS level in the water.

The basic formula for arriving at the TDS level in water is as follows.

TDS (in mg/litre) = KE (Co-relation factor) X EC (Conductivity)

KE, the Co-relation factor depends on various factors such as the nature of the liquid and the temperature of the water. It also depends on the atmospheric conditions. The value of KE ranges between 0.55 and 0.8. The reading from the electrical conductivity meter is EC.

  • The temperature of the water sample and the current pressure conditions are essential for determining the KE factor.
  • Water at around 250C and atmospheric pressure results in a KE factor of approximately 0.67
  • Water with less than 500 mg/litre is acceptable as per BIS.
  • However, water with higher levels of TDS in the range up to 1200 can be subject to water purification using RO water purifiers to make it fit for consumption.

Using this formula, you can measure the TDS levels in almost all liquids. However, each liquid will have a specific KE.

3. Using Filter Paper and a Weighing Scale

This method of measuring TDS levels in water is a conventional one. You can do it easily at home. You need not buy the electrical conductivity apparatus. Let us look at this method in brief.

Apparatus Required

  • A clean and sterilized glass beaker
  • Water sample for measuring TDS levels
  • Filter paper
  • Evaporating dish
  • A sterile stirring stick
  • Pipette large enough to collect a minimum of 50 ml
  • A weighing scale

Weigh the empty evaporating dish

Using the weighing scale, weigh the empty evaporating dish. Ensure that the dish is completely dry and free from any extraneous particulate matter. Note down the reading in mg.

Stir the water sample

Stir the water sample vigorously to ensure that the particulate matters, if any, distribute evenly throughout the sample.

Collect the water sample

Using the pipette, collect a minimum of 50 ml of water sample. Ensure that you stir the liquid continuously while collecting the sample. The particulate matter should not settle at the bottom. It will not give an accurate reading. In case you find it difficult to do so, ask your companion to keep stirring the liquid while you obtain the sample.

Extract the filtrate

Pour the water sample through the filter paper into another beaker. Repeat the procedure at least three times to ensure the collection of the entire particulate matter in the filter paper.

Weigh the evaporating dish with the filtrate

Transfer the filtrate to the evaporating dish and allow it to dry completely. Weigh the evaporating dish along with the filtrate and note down the reading in mg.

Use this formula

TDS = [(A-B) X 1000]/ml sample
(A = weight of the evaporating dish and the filtrate and B= the weight of the evaporating dish alone.)

Note that you had used 50 ml of water sample. Hence, the ml sample value would be 50 in this case. The final value of TDS is mg/litre

Ideally, the TDS level should be below 500 for the water to be fit for human consumption. However, you can use RO and other water purifiers to eliminate TDS if the TDS levels are more than 500. Any value over 1200 mg/litre is unacceptable according to BIS.

Why should you remove excess TDS?

We have seen that TDS is not a single contaminant. It is a mixture of various salts such as calcium, magnesium, and potassium among others. These salts are necessary for our good health.

However, the water sources in our country contain other undesirable impurities like the human and industrial waste. There are instances of the water sources being contaminated by arsenic, mercury, and lead as well.

These impurities can pose a health hazard. Similarly, TDS levels more than 500 ppm can also have a detrimental effect on our overall health. Therefore, you need to remove the excess TDS from the water before consuming it.

How do you eliminate excessive TDS?

You can eliminate excess TDS using three methods. Let us discuss them, in brief, to understand them better.

Distillation

This process involves boiling the water and allowing ten vapours to cool down. The resultant water is bereft of TDS as the salts remain in the boiling water solution. It is the easiest method to remove TDS.

Reverse Osmosis

Reverse Osmosis (RO) is a popular method of eliminating TDS. Almost all the water purifiers available on the market use this technique. This process involves the passage of water through a semipermeable membrane containing microscopic pores that allow molecules smaller than 0.0001 microns to pass through.

The TDS molecules are comparatively larger, and hence they get trapped in the membrane. RO is one of the best methods as it ensures complete elimination of TDS from the water.

Deionization

The deionization process involves water to pass through two electrodes (positive and negative). The ion-selective membranes enable the positive ions to separate from the water as they move towards the negative electrode. The resultant water is pure water.

However, it is better to use this procedure after subjecting the water to RO treatment. It helps to remove the non-ionic organic contaminants.

Inference

We have seen the concept of TDS and learned how to measure the TDS levels as well. We have also looked at the aspects of eliminating excessive TDS and ensuring that the resultant water has acceptable levels of TDS.

Sources: WikiHow, Wikipedia

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2comments

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1
Jyotsana Singh

Dear Shiva,

I appreciate your blog and knowledge sharing on How to check the TDS level of Water at Home?

I have gone through the section, Reverse Osmosis. The flow Diagram in Reverse osmosis section needs to be rechecked and analysed. The flow of Raw water after activated carbon filter is divided into two segments. One going in RO and Other going in UF. I need to correct you here that the Raw water should 100% pass through RO if water Purifier is RO water Purifier. If the purifier is RO+UF, then also water must pass through RO first later to UF. RO has the pore size of 0.0001 micron. TDS in totality makes Heavy metals, Fertilizers, pesticides, and more hazardous materials. These bad minerals can only be filtered out if water is passing through RO membrane. UF cannot filter out these minerals from your water source. There are few water purifiers which follow this route for water treatment just to satisfy/justify the customers taste of drinking water by adjusting TDS controller. But ethically this is wrong and need to be corrected.

2

The Groundwater Quality is not that bad in most parts of India. Unless you are living in a very polluted city or near to a chemical factory, 100% RO Purification is not required. Also, you need some important minerals like calcium and magnesium to be present in water. Some manufacturers employ TDS Controllers that allow some water directly to UV/UF Chambers without entering RO Membrane. Some manufacturers use 100% RO Purification and add minerals artificially at the end of the process, this is required if you water source is heavily polluted. Otherwise, the normal TDS Controllers are also good.