What is the hardness of water? Hard vs. Soft Water- Explained

What is the Hardness of Water? (Hard Vs Soft water- explained)

Many of you who have done some research on water filters to buy have stumbled on the word “Hard” water many times. Haven’t you?

Not only that there is a product named water softener, pre-installed at the premises of many of our houses as well. So, you can guess water hardness is an issue. 

  • Measuring the hardness of water is vital in many prospects. Understanding it can save you a fortune in dry cleaning and other maintenance.

Why? Worry not. In this article, we’ll be discussing everything about the hardness of the water. 

  • Not only that, but we’ll also shed light on the basics regarding the hard and soft water, how you can measure it, its health values, and so on.

So, let’s start.

What is hard water?

So, let’s first start with the definition of hard and soft water.

Hard water is a species of water that contains a higher concentration of Calcium and Magnesium salts or ions. On the other hand, soft water will contain those at a negligible level.

Therefore, to put it simply, we can define water hardness as the measure of the presence of Calcium and Magnesium ions in the water.

Water hardness is a very significant parameter to consider for your household.

It will directly impact your lifestyle in multiple ways. We will discuss those step by step.

Now, most of us know that the chemical formula of water is always “H2O”. That means, in a molecule of water, there will be always one Oxygen and two Hydrogen atoms.

Now, where do these Calcium and Magnesium ions come from? How do the minerals continue to mix with the water and ultimately increase its hardness?

So, let’s first know more about how the quantities of Calcium and Magnesium ions increase in water.

Let’s go.

How does soft water turn into hard water? – (Water Cycle)

So, let’s discuss how the water picks up these Calcium and Magnesium and reaches us. We’ll also find out whether we can find soft water devoid of these ions from nature.

Most of us live in big cities. As a result, we get our water through robust water treatment plants set up around the cities.

These water treatment plants collect water from natural sources like the lakes, rivers, or oceans. Most of these plants take in freshwater and then, filter out the pollutants from the water.

Now, let’s go back to the sources. The first source is rainwater. The water from the rain travels back into the storages like lakes, rivers, or oceans.

In its routes, water has to go through the soil at the surface of the earth. And, we all know that the soil contains minerals of various multitudes.

Among these minerals, various Calcium and Magnesium salts dissolve into the water. As a result, the TDS value continues to grow.

In this fashion, soft rainwater picks up salt molecules and water becomes harder by definition.

Now, you see, water treatment plants collect their water mostly from nearby lakes or rivers. 

The hard water from natural sources goes through a variety of extensive processes like coagulation, flocculation, sedimentation, filtration, and disinfection. 

After this, water becomes suitable for us to drink. But, these processes contribute little to reduce the hardness of the water.

As a result, in most cases, we get hard tap water. That means it will have a higher magnitude of Calcium and Magnesium ions.

If you’re curious about how water treatment plants work, you should visit our post here.

Rainwater Vs. River water- Which one is harder?

So, let’s answer a frequently asked question “Which one is softer? – Rainwater or River water”. You can probably guess it if you’ve read through our previous section.

The answer lies in the fascinating process of the water cycle. The water from various sources turns into vapor and enters the atmosphere.

Evaporation, transpiration, and sublimation are some of the processes that work to move water vapor into the air.

When the water evaporates and joins the air, it has to leave all the minerals in it. 

As a result, all the Calcium and Magnesium salts are left behind and cannot move into the air due to high melting and boiling points.

After that, water condenses and then, it comes back to the surface as rainwater. This happens due to condensation and precipitation.

Now, as the water vapor is in the air without any salts when it comes down as rain, it will not have any as well. As a result, the rainwater will have little to no minerals.

On the other hand, the water after rainfall will flow through the surface and move back to natural sources like lakes, fountains, or rivers.

On the way, various salts on the surface will quietly dissolve in the water. As a result, river or lake water will come with a larger quantity of Calcium and Magnesium ions. 

Therefore, which one is harder by nature? Certainly, the river water will be much harder compared to the rainwater.

If you want to discover how the water cycle works, you should take a look at our post here.

Are TDS and water hardness equivalent?

There is a common misconception regarding TDS and water hardness. Most people think they are the same thing. But, we couldn’t be farther from that.

To understand it better, we need to get a clear conception of what TDS is. TDS stands for total dissolved solids. 

We’ve already discussed that the tap water that we get regularly comes from various sources. And, because of that, the water is not always completely pure.

As a result, the water contains mineral salts with Sodium, Potassium, Calcium, Magnesium, Chloride, Sulphate, or other ions.

That’s not all the water will also contain some microorganisms- bacteria, protozoa, and many others.

TDS or total dissolved solids measure the complete quantitative amount of materials that dissolve into the water. 

Therefore, you see, measuring TDS is a downright approach to find out the dissolved solids from the water.

On the other hand, water hardness is a measure of the amount of Calcium and Magnesium ions in the water. Apart from that, sometimes we measure the number of Iron ions as well.

Therefore, we can narrow down water hardness as the measurement of only two or three specific ions rather than all the various species of chemical ingredients dissolved in the water.

We hope now you have a clear concept of why TDS and water hardness differ from each other. If you would like to know about the TDS of water, you should visit our post here.

3 possible signs by which you can detect hard water

Now, you probably have some introduction to the concept of hard water. But, the question that arises is “Can we separate hard water from soft water?”

Sadly though, we cannot visually distinguish hard water from soft water. But, there are ways which can indicate the hardness of the tap water that you’re getting.

Now, let’s take a quick look at those signs by which you can realize you’re using hard water.

Water will have a slightly odd taste

In most cases, hard water will taste somewhat odd or bitter compared to soft water. That’s because of the presence of a growing amount of Calcium and Magnesium ions.

Therefore, as soon as you find a strange sensation from drinking water, you should immediately test your tap water for its hardness.

Water spots and lime-cycles will be visible on the distribution pipes

The next thing that will be evident due to hard water is the wearing of the metal pipes in our inhouse water distribution system.

The Calcium and Magnesium salts continue to gather around the pipes and as a result, the quality of the metallic tubes deteriorate.

In most cases, at the opening of the faucet, you will see water spots. This happens due to the accumulation of Calcium and Magnesium ions around that place.

As you can see, these lime cycles or water spots are one of the primary indicators of the excessive hardness of the water.

The color of your clothing will visibly fade

Another important sign to detect the water quality, in terms of hardness, is to check the coloring of your clothes after washing with the water.

As you already know that hard water is abundant with Calcium and Magnesium ions. These ions react when in contact with soap. As a result, you don’t get fine leather.

That’s not all. The ions will also attack the coloring agents of your clothes. Therefore, if you continue to wash your clothes in hard water, the color will fade gradually.

From this prospect, you can see that if you aren’t getting a decent amount of leather in your water using soap and your clothes’ color is fading, you need to test your water right away.

How can you measure the hardness of water?

Now, that you know the signs of hard water, it is time to know how you can measure the absolute hardness of your tap water.

From the signs of hardness, you can realize it is imperative to find out whether you’re using hard water or not. Finding it out helps you in many different ways.

But, only the problem is finding out the absolute value of hardness is not so easy as it seems. You will have to go through an extensive process of titration.

If you’re familiar with chemistry, you probably have come across the term titration. In this section, we’ll discuss how you can find out the hardness of water through titration.

So, let’s take a look.

Water hardness test with titration

Apart from the sample water, You’ll need the following chemical items for the test.

Chelating agentBuffer solutionIndicator
EDTA (Ethylenediaminetetraacetic Acid)(NH3+NH4+) solution + KOHManVer indicator
  • Here we’ll be using EDTA or Ethylenediaminetetraacetic Acid as a Chelating agent. This one can react with the Calcium and Magnesium ions of the solution.
  • For the reaction to occur effectively, we’ll have to use a buffer solution that has a pH value of 10. For this, we’ll be using a Caustic Potash solution with Ammonium.
  • Last but not least, we’ll also need a ManVer indicator to mark the endpoint of the titration.

In addition to the chemical reagents, you will need the following instruments as well.

  • Burette
  • Beaker
  • Conical Flask

Now, let’s take a look at the test.

  • Firstly, you need to take 10ml of the sample water into the conical flask or beaker.
  • Then, you should add 1ml of buffer solution into the sample. This will keep the pH of the solution at a comfortable zone for the reaction.
  • Next, you need to add 2ml of the ManVer indicator into the flask or beaker. This will be used to indicate the endpoint of the reaction.
  • Remember, due to the indicator, the solution will have a red color.
  • Then, you need to fill the burette with a standard solution of EDTA (Ethylenediaminetetraacetic Acid). The concentration should be about 0.01M.
  • Now, comes the interesting part if you like chemistry. It’s time to titrate. You will continue to pour drops of EDTA solution into the beaker or flask.
  • Be careful while you’re doing this. That’s because it only takes a single drop of EDTA to end the reaction.
  • If you aren’t careful enough, you might pour more drops then required. As a result, you will be calculating the wrong value.
  • After the indicator changes its value from red to blue, the titration is complete. Now, you should measure the volume of EDTA used in the process.
  • To increase accuracy, you should follow the guideline at least two more times. Each time you should note down the volume of the EDTA solution.
  • Now, find out the average volume, Vavg of the EDTA solution.
  • After this, you can find out the absolute value of the hardness of the sample. You can find it through the following equation.

Hardness of the water, concentration of Ca2+/Mg2+ ions = (Vavg * 100) mg/L or ppm

Here, ppm stands for parts per million and mg/L stands for milligrams per Litre. In the case of a low-density solution, for example- water, both are equivalent.

In this manner, you can calculate the hardness of the tap water you’re getting. 

Are you getting overwhelmed with this much chemistry? Worry not. There are other ways as well.

You can use a water hardness test kit to comfortably calculate the hardness of the water. This can be handy for other purposes as well.

You can check those out here on Amazon.

How can you interpret the value of the hardness of water?

Now that you know the common ways to calculate the value of the hardness of your water sample, it is time to interpret those as well.

We’ve created a table showing you the various levels of hardness and their relative interpretation.

This table shows you the value based on the concentration of only Calcium Carbonate. Take a look. (McGowan, 2000)

The concentration of Calcium CarbonateInterpretation
0-60 mg/LSoft
60-120 mg/LModerately hard
120-180 mg/LHard
180 mg/L or aboveVery hard


Throughout this post, we tried to make you familiar with the concept regarding the hardness of the water.

We have done a lot of research to bring all this information into a single article. But, the topic is very extensive and you can guess that as well.

That’s why we’ll be publishing more content regarding this shortly. Until then, stay tuned.

Also, if you find this article informative, please don’t forget to share it with your peers and spread the knowledge. Cheers!!!

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