What is the difference between TDS and Hardness?- Helpful Explanation

What is the difference between TDS and Hardness?- Helpful Explanation

Water is a vital component of our day-to-day life. That’s why maintaining water quality and consuming safe and pure water is of primary concern.

The first step towards ensuring hygienic water quality is to get a clear concept of the relevant parameters. The hardness and TDS or total dissolved solids are two such parameters.

We have various water treatment equipment like water filters, water softeners, water heaters, and water distillers installed at our house. And, these tools deal closely with TDS and hardness.

Therefore, it is high time we discussed the differences between hardness and TDS of water. And, as for us, we at Aquaseep try to provide you with fresh and creative content on home improvement tools.

Now, let’s find out more about TDS and hardness.

What is the TDS of water?

TDS stands for total dissolved solids. It works to measure the amount of dissolved impurity in a liquid. The impurity includes dissolved minerals, electrolytes, and other organic compounds.

And, how do the impurities dissolve into the water? The answer lies in origin. We get our water through municipal water treatment plants. But, what is the source of water for these plants? The answer is the lakes, rivers, and in some cases, the oceans.

Water passes through vast expanses of land to reach the treatment plants. On the way, it picks up various salts from the soil, which quickly dissolves into it. And that’s how the water gets its mineral components.

Apart from the minerals, numerous organic compounds also make their way into the water. Much of which consists of organic waste. Few of those will dissolve and increase the portion of dissolved impurities.

You need to consider all the dissolved molecules in the water while measuring TDS. As we said earlier, the dissolved portion can consist of both organic and inorganic components.

The water then gets picked up by water treatment plants which get rid of a significant portion of the insoluble components. Also, much of the soluble compounds get filtered out as well.

The result is the supply of water that we get each day. Therefore, you see, the tap water will have some portion of minerals and other dissolved molecules in it.

In this context, the TDS gives you a cumulative index to measure dissolved impurity remaining in the water. So, you see, TDS (Total dissolved solids) is vital for measuring water quality.

How can you measure the TDS of water?

You can measure the TDS of a water sample in two ways: using a water test kit or boiling the water and weighing the residue waste. But, firstly, you need to ensure the water doesn’t contain any undissolved impurities.

Now, let’s discuss how both of these processes work.

Measuring TDS of water with a water test kit or TDS meter

Water test kits, to be accurate, TDS meters are the most commonly used tools to find out the TDS level of a water sample. The TDS meters calculate TDS by measuring the conductivity of water in real-time.

It is possible because pure water doesn’t conduct electricity at all. The minerals divide into ionized particles and dissolve into water. And, with their presence, water starts to conduct electricity.

TDS meters take into account this bit of info. As you dip its leads into the water sample, it will probe out the conductivity of water. And, in this fashion, you can find out the TDS of that particular water sample.

If you’re looking for a precise TDS test kit, you should check out our recommended TDS meter here. Check it out on Amazon. Here’s the link.

Measuring TDS by boiling the water and weighing the residue

A more precise way to calculate TDS is by boiling out the water. As the water leaves the sample, the only thing left will be the minerals. Consequently, weighing the residue gives you an estimate of the total dissolved solids in the water sample.

The process is pretty straightforward. But, you need to take care of a few things beforehand. 

Firstly, make sure the sample is free from dust, rust, and sediment particles. Use a carbon-block water filter to get rid of all the undissolved impurities. If you’re looking for a good water filter at a reasonable price, you should check out our post here.

After you get rid of the sediment particles, measure the volume of the sample. As the water is free of the specks of dirt, you will get the ensemble weight of water and dissolved solids.

Next, you need to take the water in an open pan or pot. Apply heat underneath. As the temperature rises, the water will start to evaporate. After all the water is gone, all that will be left is the minerals.

Now, weigh the residue. Then, using the unitary method, you can easily calculate the TDS of the sample. The equation is as follows.

TDS of sample = weight of the residue in grams/volume of the sample in liters.

In this fashion, you can measure the TDS of your water sample. But, unlike using a TDS meter, it will require a lot of time. Nevertheless, the margin of error gets significantly lower in this method.

What is the hardness of water?

Water hardness specifies the amount of Calcium and Magnesium ions in a sample of water. It works as a quantitative measurement of only Ca2+ and Mg2+ ions among all the dissolved solids. Generally, hard water suggests the sample water is rich in Calcium, Magnesium ions.

So, why are Calcium and Magnesium ions so special? That’s because the Ca2+ and Mg2+ ions modify the behavior of the water sample. As you add soap to a glass of hard water, it will create scum instead of bubbles.

How does hard water create scum? The answer lies within these two particular ions, Calcium and Magnesium. These ions react with the soap and form a layer of a froth-like precipitate.

Consequently, the soap solution loses its capacity to get rid of the dirt. And that’s why so many households resort to water softeners these days.

In addition to its reduced efficacy during washing, hard water is also a pernicious agent slowly causing damage to your plumbing system. 

So, you see, the water hardness is such a crucial parameter that helps determine the health of a water sample. You can learn more about water hardness in our post here. Check it out here.

How can you measure water hardness?

By dropping some soap solution onto the water, you can easily find out the hardness of that particular sample. If you watch scum forming instead of bubbles, you should realize the water hardness level is pretty high.

Generally, regular soaps create bubbles coming in contact with water. But, the scenario changes in hard water. As previously discussed, the Calcium and Magnesium ions in the water start reacting with the soap.

As a result, you will find a layer of scum floating around. Now, you can make use of this phenomenon to measure hardness. Just drop some soap on the sample and stir it. If you find a layer of scum instead of bubbles, it is hard water.

Although the process is simple, it doesn’t provide the value of hardness. To find out the absolute value, you need to use titration. Through this, you will be able to precisely detect the level of hardness of a sample of water.

Worry not. The municipal water suppliers usually provide the values of water hardness. So, you can check whether you’re using hard water by calling your local water helpline.

On this note, water hardness also has the same unit as TDS, mg/L.

What are the differences between hardness and TDS?

The primary difference between water hardness and TDS is that TDS measures all the dissolved solids in the water, both organic and inorganic. On the other hand, hardness focuses on a selective portion of the TDS- Calcium, Magnesium. 

As previously discussed, our regular tap water consists of various dissolved molecules. The TDS gives you a cumulative weight of all the dissolved impurities in the water. 

In addition to Calcium and Magnesium, the impurities will include Sodium, Potassium, Sulfate, Phosphate, and other ions. The value of TDS helps you understand the nature of the water sample.

According to WHO, if the TDS level is anywhere within 50 to 900 mg/L or ppm, you can drink the water. But, if the TDS value exceeds the recommended level, you should go for a water filter. 

So, you see, TDS gives you a solid perception of whether the water is drinkable or not. Meanwhile, the hardness narrows down the TDS value to only Calcium and Magnesium.

As we discussed earlier, these two particular ions will complicate your life by making it harder to wash your favorite fabrics. Moreover, Ca2+ and Mg2+ ions cause limescale to build up inside the faucets and metal pipelines.

But, hard water doesn’t affect the drinkability of water. Generally, hard water will have a hardness of 120 mg/L or above.

In a nutshell, the TDS determines whether you should drink the water or not. On the contrary, hardness determines whether you should use the water for washing clothes or not. 

To keep the TDS level in check, you can use a reverse osmosis water filter at your home. Meanwhile, water softeners should be your first choice for treating hard water.

If you’re looking for the best RO water filters, you should check out our post here. Also, you can check out our post here to find out more about water hardness.


Throughout this post, we discussed TDS and hardness- two significant parameters to assess the nature of water. The TDS evaluates the qualities of the water, whereas hardness determines the efficacy in day-to-day life.

If you would like to learn more about TDS or total dissolved solids, you should check out our post here. Also, you can find out more about hard and soft water on our post here. Check it out.

Furthermore, if you’re looking for the best reverse osmosis water filters, check out our top 10 budget-friendly choices. Check out our post here.

In this post, we pointed out the differences between hardness and TDS. If you still have some questions, feel free to leave those in the comment section.

And, finally, if you’d like to read more informative posts like this, check out our blog page here. Cheers!!!

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