Understanding Water Turbidity: 3 Important Factors to Consider while Assessing Drinking Water

Water Turbidity: An Important Concern for Climate Change!

Turbidity- An Overview, Uses, Properties and Levels of Turbidity in Different Cities across the Globe: 3 Important Considerable Factors

Understanding Water Turbidity: 3 Important Factors to Consider While Assessing Drinking Water


We all are aware of the rising concerns related to the changing climatic conditions and the drastic changes observed in the environment in terms of disruption of the seasonal cycles, heavy global warming, rising temperatures across the world and the meltdown of glaciers worldwide.

All the above-mentioned phenomena are just a fraction of the climatic variations observed on the Earth in the past decade. Under such situations, we cannot ignore the term turbidity. The term is not widely explored and come across as a common-phrase definition to many laymen. Turbidity in simple terms, refers to the hazy or cloudy effect created by minor particles exhibiting the property of light scattering. Turbidity is most commonly observed in clear liquids such as water and the light is scattered at approximately 90 degrees or more by minor particles also known as suspended particulate matter and abbreviated as “SPM”. These suspended particulate matter are not necessarily observable by naked eye, owing to their minute size and limited visibility index. These particulate matter could be in the representative forms of algae, silt, plankton or sewage residue.

Understanding the Phenomenon of Turbidity Closely

This scientific phenomenon of turbidity reflected in water is a major component or element contributing to water and air pollution. Significantly hampering the overall usability, relative quality and clarity of water, turbidity as a phenomenon raises important concerns in relation to climate change. It has been proved by several scientists that turbidity can be useful as an asset to all individuals if its scientific properties and occurrence patterns are studied and observed in detail for controlling and curbing air and water pollution. Now, the question arises of how to measure turbidity? So, we have an immediate solution for this question and doubt of ours. Many inventions and discoveries have been carried out in the past to measure several phenomena such as a lactometer is used to measure the purity of milk by measuring its density, similarly, a hydrometer is designed to measure the specific gravity of liquids by calculating the ratio between the density of the liquid and the density of water. So, in a similar manner, we measure the turbidity of water.

Measuring Turbidity using Scientific Formula

The most commonly unit used to express turbidity of water is the Formazin Turbidity Unit (FNU). ISO or International Standard Organization defines its units in terms of FNU.  ISO 7027 provides the method in water quality for the determination of turbidity. It is used to determine the concentration of suspended particles in a sample of water by measuring the incident light scattered at right angles from the sample. The scattered light is captured by a photodiode, which produces an electronic signal that is converted into turbidity. It is stated that there is a direct relationship between turbidity and water quality. By saying quality of water, we hereby refer to water pollution due to the deteriorating conditions of water bodies.

Several pollutants such as dissolved metals and pathogens can combine with the suspended particulate matter and enter into the water body. This is why an increase in turbidity can often indicate potential water pollution, not just a decrease in water quality. Contaminants include bacteria, protozoans, nutrients (e.g. nitrates and phosphorus), pesticides, mercury, lead and other metals. Several of these pollutants, especially heavy metals, can be detrimental and often toxic to aquatic life. In addition, turbidity also poses threat to human lives by reducing and eliminating the overall quality of water and making it fatal for consumption. Considering other factors, turbidity also makes the overall appearance of water as undesirable and unhygienic. The crystal clear nature of water, is essentially responsible for its attractiveness and also deemed as a sign of its safe nature. Therefore, the moment the water color is compromised, it is essentially considered to be substantially unhygienic and essentially unfit for consumption. In order to ascertain the quality of water, it is important to measure its relative turbidity levels.

The addition of nutrients can encourage the development of harmful algal blooms. The positive correlation between water pollution and turbidity is the reason why scientists initially check the turbidity level of the water for estimating the approximate intensity of polluted water. Similarly, turbidity is also related to air pollution. Like, in the above situation, how dissolved metals and pathogens combine with suspended particulate matter, in the same way, aerosols combine with the suspended matter and disrupt the occurrence of solar irradiation and lead to air pollution. As a result of the relation existing between aerosols and attenuation of solar radiation reaching the Earth’s surface, various turbidity factors based on radiometric methods have been defined to evaluate atmospheric turbidity. These factors include the Linke turbidity factor (TL), the Ångström turbidity coefficient, the Shueppe turbidity coefficient, and the Unworth-Montath coefficient. The amount of atmospheric turbidity or turbidity of air depends on the atmospheric aerosol load. Aerosols are defined as the minor solid or liquid particles present in air which vary in size from 10 to the power -3 to tons of microns.

Turbidity Levels in Cities Situated Across the Globe

Moving on, let us talk about the turbidity levels in cities situated across the globe.  For most mangroves along the eastern coast of Australia, in particular, Moreton Bay, turbidity levels as high as 600 Nephelometric Turbidity Units (NTU) are needed for proper ecosystem health. The U.S. Environmental Protection Agency (EPA) has published water quality criteria for turbidity. These criteria are scientific assessments of the effects of turbidity, which are used by states to develop water quality standards for water bodies. (States may also publish their own criteria.) Some states have promulgated water quality standards for turbidity, including:

  • Louisiana. 25, 50 or 150 NTU, or background plus 10 percent, depending on the water body.
  • Vermont. 10 NTU or 25 NTU, depending on water body classification.
  • Washington. 5 NTU over background (when background is 50 NTU or less), or 10 percent increase when background is over 50 NTU.

Additionally, the World Health Organization (WHO) has established the drinking water turbidity level to be not more than 5 NTU and ideally below 1 NTU.


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