TDS is a common term that you will come across while deciding to purchase water purifier for home. There is lot of confusion about what is TDS and what are the acceptable levels of TDS. In this article we will clear all these doubts.
What is TDS?
TDS stands for Total Dissolved Solids. It is the amount of metals, impurities, salts, minerals and other types of particulate present in water.
Whenever water comes in contact with a solvent, some of its particles get absorbed in water. TDS can come in water through many possible ways. Some part of TDS is natural, while some is because of human activities.
Naturally occurring minerals and salts give the familiar taste to drinking water. While, TDS through external activities can be quite harmful. Impurities can enter water through the chemicals used in sewer systems, or it can enter through road salts and fertilizers, it can even enter through the plumbing that takes place at your house.
Why is the importance of TDS?
If TDS is mostly impurities, then should we not try to remove it completely, right? Wrong. Some level of TDS is necessary because of following reasons:
- TDS can be due to natural minerals and salts required for healthy body. Deficiency of these minerals and salts can lead to health issues.
- Smaller levels of TDS lends natural taste to water. Water with 0 TDS can taste unnatural or even bitter.
As you can see, some level of TDS can be useful. On the other hand, higher level of TDS can be harmful for our body. This brings us to our next question: What are the acceptable levels of TDS?
What is safe TDS limit?
There is a limit to how much minerals, salts, metals and other impurities, should be present in water, so that it is safe for you to drink.
TDS is measured in milligrams per liter (mg/l), or parts per million (ppm). The easiest way to measure the TDS level is through TDS meter.
Secondly, anything that has the measurement of 900-1000 ppm or higher is considered as an unsafe level of TDS.
It’s important to note that if the amount of TDS is more than 2000 ppm then majority of water purifiers can’t handle it.
Acceptable TDS levels in India
|TDS Levels (mg/litre)||What it means|
|Less than 50||Very low level. Lacks natural minerals and salts necessary for human body.|
|50 to 150||Acceptable. Decent levels but still may not be sufficient.|
|150 to 250||Healthiest. Best for your heart.|
|250 to 350||Acceptable. Usual range for groundwater in India.|
|350 to 500||Acceptable. As per BIS recommendation.|
|500 to 1200||Not Safe. RO water purifier is recommended.|
|Above 1200||Not Safe. Advanced RO water purifier with multi-stage filtration is recommended.|
WHO recommendation of TDS less than 300 is for palatability. It means water will taste more natural and easy to drink if TDS is less than 300.
Palatability of drinking water as per WHO:
|TDS Level (ppm)||WHO Recommendation|
|300 – 600||Good|
|600 – 900||Fair|
|900 – 1200||Poor|
How to Check TDS Level at Home?
There are 3 methods to check TDS levels. First method is using a digital meter. This is the easiest, inexpensive and most convenient method.
1. Digital TDS meter
TDS meter is a small handheld device that quickly finds out TDS once you dip it inside water. It comes in as low are Rs 200.
What are the things you need?
- Digital TDS meter.
- Glass / bowl of water with at least 2 inches of depth.
Steps to use TDS meter
- First, remove the protective cap
- Turn the TDS meter on by pressing the switch located on the panel.
- Immerse the meter into the water. (do not immerse beyond max immersion level which is usually 2 inches).
- Stir the meter lightly to remove any air bubbles.
- As soon as you immerse it, the reading will fluctuate. It will tale around 5 to 10 seconds for the reading to stabilize. once it stabilises, you can press HOLD button and take it our of water to view conveniently.
- The level is usually in ppm, but if it has x10 symbol, then multiply the reading by 10 to get the levels in ppm or mg/l.
- You can shake off excess water from the meter once you have used it and replace the protective cap.
Precautions to be taken while using TDS meter
- Make sure not to dip the TDS meter beyond safe level because there are chances that water can enter the meter and damage it.
- Do not expose the TDS meter to intense heat or direct sunlight so that the meter will last long.
2. Filter paper and weighing scale
You can find out the TDS of water using a simple filter paper and weighing scale used in home.
Basic principle to calculate TDS through this methods is that if we can find the weight of the impurities in water, we can divide this weight by volume of the water to get TDS in mg/L (ppm).
Apparatus required to measure the TDS
- A beaker with water sample.
- Filter paper.
- A weighting scale.
- An evaporating dish.
- A stirring stick.
- A pipette with minimum capacity of 50ml
Steps for measuring TDS with filter paper and weighing scale
Here are the steps:
- Take the weight of the empty evaporating dish. Note this measurement in milligrams as “A” and move on to next step.
- Stir the water in the beaker with the help of the stirring stick properly. This will dissolves the impurities evenly so that we can get close-to-accurate reading.
- Collect 50 ml of the stirred water into the pipette.
- Allow the water from the pipette to pass through the filter paper and let the sediments collect on the it. Repeat the procedure few times so that almost all the impurities are deposited onto the sand paper.
- Now transfer all the contents of the filter paper to the evaporating dish and let it dry completely.
- Now weigh the evaporating dish containing the sediment. Note this measurement as “B”.
Now, to calculate the TDS, use this formula: TDS = [(B-A)*1000]/[volume of water in litre]
Here B is the weight of evaporating dish along with the sediment in milligrams. A is the weight of empty dish in milligrams. And volume of water is 50 ml, which is 0.05 litre.
So the final formula in this case is: TDS = [(B-A)*1000]/0.05
This value will be in mg/l which is also referred to as ppm.
- Take due care while weighing the evaporating dish.
- Before weighing the dish make sure that the filtrate is totally dry.
3. Electrical Conductivity Meter
The electrical conductivity meter is one of the lesser used methods. It works by passing electric current through the water and measuring the resistance.
Apparatus required for measuring the TDS.
- A clean glass beaker.
- Water sample heated at 250 degree Celsius.
- An electrical conductivity meter.
Steps for measuring TDS with electrical conductivity meter
- Pour the water into a clean glass beaker.
- Switch on the conductivity meter and insert its measuring lead into the water.
- As soon as you insert the lead, the reading will fluctuate for few seconds
- Wait for the reading to stabilize and note down the reading.
- This value indicates the purity of water.
This is electrical conductivity and the value is measures in µS (micro siemens)
Another thing that you need to understand about is KE or Co-relation factor. Its value depends on nature of the liquid, water temperature and atmospheric pressure. The value of KE ranges from 0.55 to 0.8. Water at around 250 degree Celsius is usually around 0.66. You may use this value.
Now, to calculate the TDS, use below formula.
TDS = KE (Co-relation factor) X EC (Conductivity)
This value will be in mg/l
How to buy a water purifier based on TDS levels?
For buying a water purifier, you should be aware about TDS level, and type of impurities present in water. There are many types of water purifiers – RO, UV, UF, UV, Candle-based.
|TDS Level||Muddy Water||Presence of Germs||Ideal Water Purifier|
|Less than 500 PPM||No||Yes||UV|
|Less than 500 PPM||Yes||Yes||UV+UF|
|Less than 500 PPM||No||No||Candle-based|
|Less than 500 PPM||Yes||No||UF|
|Above 500 PPM||No||No||RO+TDS Controller / Mineralizer|
|Above 500 PPM||Yes||Yes||RO+UV+UF+TDS Controller / Mineralizer|
|Above 500 PPM||No||Yes||RO+UV+TDS|
Controller / Mineralizer
|Above 500 PPM||Yes||No||RO+UF or|
RO+UV+UF TDS Controller / Mineralizer
As you can see, you do not need an RO water purifier if TDS level of your water is less than 500. (Some water purification brands cap this level at 200 PPM). If TDS is higher, then you should use RO water purifier with a TDS Controller or a Mineralizer.
This is because RO reduces the TDS by upto 90%, which can be less than safe levels. A TDS controller or Mineralizer removes this drawback by adding essential minerals back into the water.
Frequently Asked Questions (FAQs)
What is the ideal TDS required for healthy water?
TDS level between 150 and 250 is the healthiest.
Does water softener lower TDS?
No, water softeners do not reduce the TDS of hard water
Now that you are familiar with the concept of TDS, you are aware that a lot of it can be extremely harmful for your health. So, the amount of impurities present in the water should not exceed 1000 ppm and the safest, purest level of TDS present on the water is 300- 500 ppm.