Water Treatment 101: How Do We Get Our Tap Water?

Water Treatment 101 -(How do we get clean tap water?- illustrated)

One thing that we most certainly do every day is drinking water. But, have you ever wondered where this water comes from?

Does it come directly from the ocean, river, lake, or somewhere else? Why do we have to pay for tap water?

  • More than 70 percent of people don’t have a clear concept of how we get tap water. 

Huge water treatment plants are working round the clock to deliver us fresh and clean water. But, what’s inside those? 

  • We also answer one frequently asked question. Why would I need a water filter if I am already using clean and fresh tap water?

So, if you’re curious enough, let’s go and find out what is happening behind the curtain.

What is water treatment?

By now, we have already quoted the word “water treatment” many times. So, what is water treatment?

  • In short, water treatment is the way to produce clean water from natural sources. It is the process in which municipalities all over improve the quality of drinking water for its citizens.

From ancient times, people have been using water purification to some extent. Before, it was quite simple. Most conventional ways tend to meander around boiling.

Also, those who couldn’t afford would use a sieve to filter out the clay or sand particles.

But, with the advance of science, there has been a major shift in water treatment technologies all over the world.

Nowadays, you will see huge water treatment plants near big cities, even most smaller ones as well. 

Lots and lots of civil and mechanical engineers are working to provide us safe and pure water. 

Although the process has become more and more complicated over the years, the main objective is still the same.

So, what is that?

  • The goal is to remove the pollutants and harmful chemicals from natural water. Furthermore, it also aims at stripping the water of the odor and bad taste as well.

Now, that we know about what is water treatment, let’s find out why it is so vital.

Why is water treatment important?

  • Water supply is one of the top utilities alongside electricity and the internet. 

We are so accustomed to these at such an extent that we only feel their presence only when they aren’t available.

That’s why most of us don’t realize the importance of water treatment. So, let’s find out why municipal water treatment is important?

  • You probably know that water can be of two types based on their source. One is surface water while the other is the groundwater.

Whatever the source, the water is never in its purest form. Freshwater always contains impurities to some extent.

Take the lake water as an example. As the lake flows over vast areas and as a result, a huge number of components get mixed along the way.

Most of those are clay, sand, or dust particles. Besides, pesticides or other chemicals might also come into contact, depending on the regions where the water flows.

Consequently, the water quality drops. So, if we drink or use lake water directly, it might cause major health concerns.

  • Another major source can be underground water. Nowadays, most cities use strong submersible pumps to pull out water from underneath.

But, this water also holds clay particles as well. Therefore, we can’t drink or use natural water directly.

So, be it surface water of groundwater, water needs to be purified to a certain level. 

  • That’s why Govt. allows thousands and thousands of taxpayers’ money in water treatment projects each year.

I hope this paragraph clears out some of your queries about municipal water treatment. Now, let’s learn the whole process.

What are the fundamental stages of water treatment?

As we’ve mentioned earlier, the process of water treatment has become more and more complicated over the years.

But, the underlying methodology remains the same.

There are five basic stages in the complete water treatment process.

Those are-

  • Coagulation
  • Flocculation
  • Sedimentation
  • Filtration
  • Disinfection

Now, let’s look more into these step by step.

How does Coagulation work?

The process kicks off with a chemical process named “Coagulation”.

In this process, some special chemicals get mixed with water. The water contains various dust, clay, and other impurities.

According to chemistry, they are colloids. These colloids have negative charges on them. As a result, two colloid particles can never unite, but rather repel each other.

To neutralize the negative charges, treatment plants free some chemicals.

One of these special chemicals is Alum or Aluminium Sulphate. 

When Alum comes in close contact with water, it decomposes and frees Aluminium ions.

These ions have positive charges. As a result, they take in those colloids that have opposite charges on them.

In this way, the colloids fall short of their charges. Now, they quickly pile up with each other and create small groups, which we call micro flocs.

This is how coagulation works. But, the whole process needs more than that.

To ensure all the colloids are in micro-flocs, plants will mix Alums periodically. As more and more coagulants get mixed, it creates more and more micro-flocs.

Furthermore, the pH of the water also needs to remain at a certain limit to ensure maximum efficiency.

For example, for Alum to work, the pH level must remain within 5.5 to 7.5. If plants use some other chemicals, the pH limit might change accordingly.

So, this is how coagulation pans out. 

And, if you would like to know more about what pH is, you should visit our post here.

How do coagulation and flocculation work?

How does Flocculation work?

Flocculation is the next stage of all the conventional public water treatment plants.

In the previous section, you saw how coagulants create micro-flocs of colloids. In this stage, the mixing process reaches the next level.

The coagulation process slows down if water remains still. That’s why in this stage, plants continue to stir the water.

As a result, more and more micro-flocs come close to each other and collect together to form pin-flocs.

This whole process goes on, on, and on. In turn, the size of flocs continues to grow and those get bigger and heavier.

To aid in this process, plants mix polymer-like chemicals with the water. These substances make sure the flocculation process goes smooth.

Also, plant operators keep a sharp lookout for the pH level and mixing speed. If the speed exceeds a certain limit, the flocks might break apart.

In this fashion, flocculation works and creates groups of colloids. Here’s a diagram showing you the coagulation and flocculation stage in a water treatment plant.

The water remains in the flocculation chamber for about 15 to 20 mins. The duration might vary from plants to plants due to the coagulants used.

Again, if you would like to know more about what pH of drinking water means, you should visit our post here.

How does sedimentation work?

The next step for any public water treatment plant is the sedimentation stage.

You probably already know what sediment is. If you don’t know what it is, no problem. We’ll be explaining it here.

Take a glass of water. Now, pour some sand in it. Stir and mix those to create a solution.

Now, put down the glass and wait. After some time, you will see that the sand particles have settled down at the bottom of the glass.

The water also looks clean. We call this process as sedimentation, and sand particles are the sediments.

In the real world, there will be more particles other than just sand. Clay, rock, dust, and many other particles fall into the same category.

In the water treatment plant, we will call the flocs as the sediment.

As we’ve previously seen, at the flocculation stage, most of the colloids form flocs with the help of coagulants. 

At the end of flocculation, the water comes into the sediment chamber, where the velocity reaches the minimal value.

As there is no turbulence, the flocs start to settle down. They start to gather at the bottom due to their size and weight.

When bulks of flocs start accumulating at the bottom, we call them sludge. And, consequently, the bottom of the sedimentation chamber is the sludge zone.

In this fashion, most of the flocs get reduced to sludge at the end of sedimentation. And, the water also gets its purity back to some extent.

But, the water treatment process is still not over. Then, water enters the filtration stage for further cleansing.

One important reminder that water must remain at its lowest speed to obtain maximum sedimentation.

How does sedimentation work?

How does filtration work?

Filtration is one of the crucial stages in all the public or industrial water treatment plants.

After the sedimentation, most of the flocs settle down as sludge. But, there are still micro-flocs in the water which need cleansing.

The filtration stage works to make it happen. It consists of several layers of different particles. So, let’s look more into these.

In the filtration chamber, there are consecutive layers of anthracite, sand, and gravel. They work as a unit to trap the remaining flocs in the water.

As the water seeps through the layers, its speed continues to decrease. And, the microscopic flocs start to get trapped between the different layers.

This happens as the molecules in the layers are so very dense. As a result, the water molecules can pass through them. But, the flocs fail. 

That’s because the microscopic flocs are bigger in sizes than the water molecules.

Consequently, as water flows through the layers, colloids, and flocs get absorbed gradually in the anthracite, sand, or gravel layers.

During this process, some of the flocs might break down and might cause difficulties during filtration. This might reduce efficiency.

Therefore, some polymers are freed to attract micro-flocs and form bigger flocs. This helps in the total purification process.

So, you can see this bulk filtration process differs from the household purification steps. If you would like to know about household water filters, you should visit our post here.

In this fashion, the filtration chamber works and gets rid of most of the known pollutants. After this, water goes into the disinfection layer.

How does disinfection work?

The final one among the five stages is the disinfection chamber. Its function is to remove the harmful micro-organisms that remain in the water.

Various types of organisms can get through the previous four stages of purification.

Among those, some bacterias, viruses, and protozoa are the prominent ones.

If these tiny life-forms continue to remain in the water, they can cause various water-borne diseases. Therefore, public water treatment plants enforce sterilizer as a top priority.

In households, we boil water to get rid of those harmful organisms. 

But, for public water treatment, this is not a viable option. Boiling millions of gallons of water would significantly increase operating costs.

Hence, they use some other techniques. Among those, Chlorination is the most widely used one. 

What does that mean? In Chlorination, plants add some special chemicals that contain Chlorine.

These chemicals free Chlorine when those come in contact with water. 

Chlorine works as an oxidation agent and kills harmful bacterias and viruses.

There are other techniques as well. For instance, some plants use ozonation to remove harmful life-forms.

Apart from these, there are other ways like UV sterilizer. In these, ultraviolet rays attack the virus and bacterias. As a result, they lose their ability to reproduce.

But, the usage of UV sterilizers can be costly and also requires regular maintenance. 

Another less used disinfection process is over-liming. In this process, plants mix minerals to change the pH level of water. 

This results in destroying most of the harmful bacterias.

In this fashion, disinfection pans out and then, the water becomes drinkable.


Water treatment plants play a vital role to ensure safe health for the citizens.

And, through the distribution systems, water enters our houses and we get clean and fresh tap water.

We tried our best to elucidate some of the concepts that are behind the complete process. We hope this was up to your expectations.

If you would like to know about household water filtration, you should visit our post here. In this one, we’ve shed light on various steps in household water filtration.

Don’t forget to share it with your peers, as they say, “Sharing is caring!!!” Cheers!!!

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