How water is purified

Water being tested in a lab to represent how water is purified

The Water Purification Process

Water purification is one of the most important processes used in our modern society. It is the process of removing undesired impurities from water. These impurities can include chemical compounds, organic and inorganic materials, and biological contaminants. So it is a vital process to ensure the safety of your drinking water. This is why we decided to take a look at how water is purified so that you know what goes into making water safe to drink.

Methods of Purification

Broadly speaking there are four methods to purify water. They are boiling, filtration, distillation, and chlorination. Each of these methods works in different ways to purify water, we will look at each method in more detail below.

How water is purified: Boiling

Boiling water is a cheap, and natural method to purify your water, which will ensure it is safe to drink. This method will kill off any germs and parasites that may occur in the water, as these microorganisms cannot survive the prolonged heat of boiling water.

This method is easily accessible as all it requires is a stove, fire or other strong heat sources, and a pot. You then bring the water up to a rolling boil and let it boil for 1-3 minutes. If you live at high altitudes it is advised to boil the water for longer, adding a minute for every 1000 feet above sea level. This is because the boiling point of water is lower at high altitudes, so the extra time helps ensure the water’s purity. Once it has boiled for the necessary time, let the water cool, and allow any solids to settle on the bottom. Pure drinking water can then be taken off the top.


Another effective method of purification is filtration. This method uses different filter mediums to remove impurities from the water. This utilises both physical and chemical processes.

In this method, the water is allowed to flow through a physical medium, like sand or sponges, which catches all physical impurities in the water. The water then proceeds through progressively finer filter mediums, that prevent bacteria and other microorganisms from passing through. Filtration can also use chemical filter mediums like activated carbon, and other chemicals that absorb impurities from the water. Once the water has passed through the filter all impurities are removed and trapped in the filter leaving you with clean purified water. Filtration is a commonly used method for large-scale water purification, as it uses little energy, and is very cost-effective.


Distillation is another method to purify water that uses heat. This method is based on the fact that the boiling point of water is lower than any contaminants found in water.

In this method, the contaminated water is brought to a boil and left to boil till the water vaporises. The water vapour is caught and directed into a condenser, where it cools and reverts to liquid water. This water is completely pure and safe to drink, as all of the impurities are left as sediment in the pot.

This method is very effective for obtaining pure water. However, it is quite an energy and time-intensive process. This is why it is mostly used to purify small amounts of water, as it is not ideal for large-scale water purification.


Chlorination is the process of adding chlorine to the water to purify it. Chlorine is a powerful chemical, that kills germs, parasites, and other disease-causing organisms in the water. Making the water clean and safe. Chlorine is a cheap and effective option for purifying water, which is why it is used in municipal water purification plants around the world. 

How water is Purified in Nature?

In nature, water is purified through three methods we will discuss below.

  1. The water cycle

The water cycle refers to the natural evaporation of water, mostly from the oceans, into the atmosphere, which then falls as rain. Rainwater is naturally purified as the impurities are left behind when the water vaporises. It is worth noting that with pollution in the atmosphere rainwater can pick up other impurities as it falls. Therefore if you wish to drink rainwater it is advised to use the aforementioned purification methods, to be safe.

  1. The Soil

Soil naturally purifies water as well. It does this by acting like a filter. As the water falls through the different soil layers impurities and particles get left behind in the soil while the water percolates down. The water is purified further by bacteria and microorganisms in the soil that break down contaminants and chemicals in the water. This is why groundwater is often safe to drink, however, it is always advised to test groundwater before drinking it.

  1. Wetlands

Wetlands are often called ecological kidneys, as they have three methods of natural water purification. These methods are sediment trapping, nutrient removal, and chemical detoxification. Though these methods do purify water it does not mean the water in wetlands is safe to drink, as there are microbes in the water that can be harmful.

Sediment trapping is caused by the dense plant life in wetlands, which slows the flow of water through them. The slowed water allows impurities to sink to the bottom of the wetland. There over time, they settle deeper into the ground which sequesters them from the environment.

Nutrient removal is the process where pollutants like phosphorous and nitrogen are captured by the wetlands. These pollutants are taken up by wetland plants, preventing them from flowing into larger bodies of water like rivers or lakes.

Chemical detoxification refers to the removal of toxic chemicals that occurs in wetlands. These pollutants are removed in multiple ways. They can be trapped in settled soil particles and become buried in the sediment. They may also be converted into less harmful chemicals by biological processes in the wetland, or exposure to the sun. Plants can also absorb some of these chemicals as well.


We hope this has given you a better understanding of how water is purified. As well as how you can purify water should the need arise. So that you know how to ensure your water is safe to drink. As well as giving you a greater respect for the natural processes that help to purify the water of the world.

Source: ScienceDirect

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