How Are Impurities Removed From Water?

Water purification is the process of removing impurities from raw water to make it safe for human consumption. There are several methods that can be used to achieve this, including physical, chemical, and biological processes. Depending on the source of the water and its intended use, any combination of these processes may be used in order to make it suitable for drinking.

Ways To Remove Impurities From Water

Physical Processes
Physical Processes

Physical Processes: Typical physical processes used in water purification are filtration, sedimentation, and distillation.

  • Filtration involves passing the water through a medium such as sand or activated carbon to remove suspended particles from the water.
  • Sedimentation is used to reduce turbidity (cloudiness) by allowing time for heavy particles to sink and be removed.
  • Distillation works by boiling the water and collecting the vapor in a separate container, leaving the impurities behind.
Chemical Processes
Chemical Processes

Chemical Processes: Chemical processes involve using chemicals to remove or bind particles in order to make them easier to remove by filtration. Common methods include coagulation, flocculation, and chlorination.

  • Coagulation is achieved by adding chemicals such as alum which causes suspended particles to stick together, forming larger and heavier particles that can then be removed by sedimentation or filtration.
  • Flocculation is similar but instead of adding chemicals to the water, mechanical mixing is used to cause particles to clump together.
  • Chlorination involves treating the water with chlorine which combines with impurities and forms a compound that can be easily filtered out. Chlorine gas is added to the water to kill any viruses or bacteria present in the water. This method can also help reduce turbidity by breaking down suspended particles and organic matter.
  • Ozonation involves passing ozone gas through the water, which helps remove contaminants and also improves the taste and odor of the water.

Biological Processes: This process utilizes living organisms to remove impurities from the water. The most common type of biological process used is called activated sludge, where bacteria are added to the water and help break down organic matter. This creates an environment where other naturally occurring bacteria can help purify the water. Other biological processes include slow sand filtration and constructed wetland systems, both of which use natural microorganisms to break down pollutants in the water.

Other Methods To Treat Impure Water

Boiling the water

Boiling: Boiling is a simple, effective way to purify water. This process involves heating the water until it reaches its boiling point, which kills any bacteria and other microorganisms present in the water. Boiling also helps reduce turbidity by removing suspended particles from the water.

Activated Carbon Filters
Activated Carbon

Activated Carbon: Activated carbon treatment consists of passing the water through a bed of activated carbon. The carbon absorbs impurities from the water, and this process can also remove bad odors and tastes from the water. 

Reverse osmosis systems
Reverse Osmosis

Reverse Osmosis: Reverse osmosis is a method that involves forcing water through a semi-permeable membrane to remove impurities. This process removes salts, inorganic molecules, and other contaminants from the water.

Ultraviolet Disinfection: Ultraviolet (UV) disinfection is used to kill bacteria, viruses, and other microorganisms present in the water. A UV lamp is used to emit ultraviolet light, which kills the microorganisms.

Membrane Filtration Processes
Membrane Filtration

Membrane Filtration: Membrane filtration is a type of filtration that involves passing water through a semi-permeable membrane to remove particles such as suspended solids and bacteria. This process is commonly used to remove viruses, protozoa, and other microorganisms from the water.

Ion exchange filtration
Ion Exchange

Ion Exchange: Ion exchange is a process where the impurities in the water are exchanged for other ions. In this process, positively and negatively charged ions bind to the impurities and form complexes that can be removed from the water. This method can also remove heavy metals such as lead, mercury, and arsenic from the water.

Ultrafiltration Membrane Filters
Ultrafiltration Membrane

Ultrafiltration: Ultrafiltration involves passing the water through a membrane with tiny pores that are small enough to remove impurities from the water. This method is often used to treat wastewater, as it can remove particles such as bacteria, viruses, and other microorganisms from the water.

Desalination: Desalination is a process that involves removing salt and other impurities from seawater. This process can be done using methods such as reverse osmosis, distillation, and electrodialysis. The resulting water is free from most of the salt content present in seawater.


What Are Water Impurities?

Water impurities are any substance present in water that makes it unsafe to use for drinking, bathing, or cooking purposes. Water can contain a variety of different types of impurities ranging from industrial pollutants to naturally occurring minerals and sediments. Impurities can range from being completely harmless to extremely hazardous, depending on the type and concentration.

What Are Soluble And Insoluble Impurities In Water?

Soluble impurities are those that can be dissolved in water and include minerals, salts, and other chemicals. These types of impurities lower the quality of drinking water and can affect its taste, color, or odor. Common soluble impurities found in water are calcium carbonate, magnesium sulfate, sodium chloride, and potassium iodide.

Insoluble impurities are those that cannot be dissolved in water and include particles of sand, soil, clay, or dust. These impurities can cause physical damage to pipes or other parts of a water system if they remain suspended.

What Can Be Removed From Water In The Process Of Desalination?

What Can Be Removed From Water In The Process Of Desalination
The Process Of Desalination
  • Salts and minerals
  • Chlorine
  • Bacteria and other microorganisms
  • Metals and other inorganic contaminants
  • Organic compounds such as pesticides, herbicides, pharmaceuticals, fuel residues, and plastics
  • Dissolved gases such as carbon dioxide and oxygen
  • Radioactive particles
  • Inorganic compounds such as nitrates, sulfates, and phosphates.
  • Total dissolved solids (TDS).
  • Dissolved organic matter (DOM)
  • Bicarbonate ions and dissolved organic carbon (DOC)
  • Suspended particles such as dirt, dust, silt, and clay.
  • Heavy metals such as arsenic, lead, and mercury.


Impurities can be removed from water through a variety of methods. Each process has advantages and disadvantages depending on the level of purity desired and the type of contaminants present in the source water. It is important to consider the effectiveness of the method in removing different types of contaminants before selecting the appropriate treatment for a particular water supply.

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