Does water color indicate the presence of pollutant ?

Pure water is an inorganic compound composed of two hydrogen atoms and one oxygen atom. It is colorless, tasteless, and transparent. However, in nature, pure water is rarely found because it can dissolve certain gases, and minerals, which makes the water impure and causes it to have some water color.

It is important to note that not all colored water is harmful. In this blog, we will discuss when colored water can be harmful and which colors may indicate harmful substances.

Common impurities found in water that can affect its color

Dissolved organic matter from decaying vegetation, as well as some inorganic materials, and growth of algae and aquatic micro organisms, can all contribute to the color of water. This color can be classified as either apparent or true color. True color is caused by the presence of dissolved particles, while apparent color is caused by suspended particles.

Effect of water color

Apparent color in the water has psychological effects and makes the water displeasing. But true color may impact some negative property to the water.

  • Aesthetically displeasing: When water has a strange color, it can make people feel uncomfortable and think that the water is not clean. This can affect their emotions and make them believe the water is not good to use or drink.
  • Washing and dying: Due to iron oxide water get reddish color and this water can not be used for washing and dying
  • Carcinogenic: Some color causing organic compounds react with cl to form carcinogenic effect.
  • Chlorine demand: Increases cl demand as cl is a strong oxidizing agent it participates in redox reaction.
  • Taste and odor: Phenol like organic compound reacts with cl to induce taste and odor.

Measurement of color

To measure the color of water, a common technique is to use a tintometer which compares the color of the water sample to a standard sample. Place the sample in a Nessler’s tube. The resulting color of the water represents the True Color Units (TCU).

To obtain the TCU, add a small amount of platinum in the form of chloroplatinate to one liter of pure water. This forms the standard sample against which the test sample is compared. The tintometer is then used to determine the TCU value of the test sample based on its color compared to the standard.

Acceptable limit of color is 5 TCU and cause for rejection is 25 NTU.

Can water be made clear by removing impurities

We can not make water colorless or purely clear it is next to impossible. Because a blue color is impart in water due to water molecules absorbing the red end of the spectrum of visible light. But the color due to the foreign particle that present in water can be removed by using various treatment process.

  • Boiling: Apparent color of water remove by boiling it.
  • Coagulation: Colloidal impurities remove from water in the process of coagulation.
  • Filtration: Dissolve substances remove from water and it makes the water clear.
  • Activated carbon filtration: It works in the principle of adsorption. Impurities get attach in the surface of activate carbon and make the water clear
  • Reverse osmosis filtration: Effective at removing a range of colors from drinking water and makes the water safer and tastier.


Water acquire colours when it contact with decayed leaves, minerals, organic content etc. It may be or may not be harmful to human every times. But colour in the water has psychological effect and makes the water aesthetically displeasing. Before using it treatment is necessary. Tintometer use to measure the colour of water. And unit of colour is True Color Unit (TCU).

  • Aesthetically displeasing: Look of that water is not acceptable
  • True colour unit: $1mg$ of platinum in the form of chloro-platinate ion add in $1lit$ of pure water.

This article was crafted by a group of experts at eigenplus to ensure it adheres to our strict quality standards. The individuals who contributed to this article are:


Suprabha Panda


She is an assistant professor with masters in Environmental Engineering.

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