Turbidity Of Drinking Water

by | Dec 29, 2023

Turbidity of Drinking Water

Turbidity is a measurement of cloudy or hazy water that is often created by silt, slit, and organic matter in water. Turbidity includes suspended materials, harmful agents, and turbid water as risks. Water clarity is affected by this phenomenon. 

The amount of light scattered by these particles in the water measures turbidity. High turbidity levels can be visually recognized by reduced transparency. This impacts the appearance and safety of drinking water. 

Elevated turbidity can cause infections by promoting microbial growth. Turbidity testing is important in detecting a contaminant/pollutant in water. Knowing turbidity and safe drinking water go hand-in-hand. 

Water treatment involves monitoring and maintaining the turbidity level on a constant basis. These also form part of the quality assessment processes.

CC: Atlas Scientific

The Main Reasons For Turbidity

In order to counter turbidity, we must know the main reasons behind it. These reasons may arise due to natural as well as man-made problems.

Here are the main causes of turbidity in water:

1. Natural Erosion

Rainfall, wind, and natural processes dislodge soil particles into water bodies, increasing turbidity.

2. Land Development

Construction activities and urbanization disturb land surfaces. The disturbance causes sediment runoff into water sources which results in turbidity.

3. Agricultural Practices

Runoff from farms carries fertilizers, pesticides, and organic matter, leading to elevated turbidity levels.

4. Industrial Activities

Mining, manufacturing, and industrial discharges introduce pollutants and sediments, impacting water clarity.

5. Waste Disposal

Improper waste disposal contaminates water, escalating turbidity levels.

Harmful Effects Of High Turbidity

Turbid drinking water causes diseases to humans and also the ecosystem. Water pollutions and consequent health hazards are manifested high levels of suspended solids in water.

1. Pathogen Presence:

High pathogen presence is often a result of high turbidity in water. This increases the threat of infections arising from the poor water quality. The pathogens may lead to chronic diseases such as cholera, diarrhea, tuberculosis, etc.

2. Disinfection Challenges:

Elevated turbidity hinders disinfection processes, lowering the effectiveness of chemical treatments.

3. Ecological Impact:

Reduced water transparency in water bodies is very harmful to marine life. This is mainly because sunlight is unable to penetrate turbid water.

4. Reduced Water Clarity:

Transparency is a symbol of pure water, which is not the case when turbidity is high. High turbidity affects water transparency, impacting its aesthetics and making it visually unappealing.

Addressing high turbidity is a critical component of water purification. It protects the public from water-borne diseases, maintains a balanced ecosystem, etc. To maintain the Quality of water, constant testing is required. 

Public health protection, on the other hand, needs appropriate treatment based on the test results. Mitigative methods should be put in place to ensure that water quality standards are upheld, and the general public is protected.

Safe Standards Of Turbidity

Here is a depiction of turbidity standards laid down by various reputed organisations:

ParameterSafe Standards (NTU or Nephelometric Turbidity unit)
AestheticsBelow 1 NTU
Drinking Water (BIS)5 NTU as per IS 10500
World Health Organization (WHO) GuidelinesLess than 5 NTU
Environmental Protection Agency (EPA) StandardsMaximum of 0.5 NTU (SMCL)

Safe turbidity standards vary slightly among different regulatory bodies. To enhance the beauty and ensure clearness, aim for turbidity below 1 NTU. 

Organisations like WHO and EPA define standards of turbidity with regard to their research and survey. Although the WHO suggests a standard of 5 NTU, it is on the higher side of the safety limit. You should aim for the Indian standard i.e. 1 NTU.

Observing these standards guarantees us pure drinking water. These standards not only satisfy health/safety requirements but also contribute towards building a health-conscious society.

How To Test Your Water For Turbidity?

Turbidity tests are necessary as an indicator of water clarity and possible contaminants. There are several techniques including self-made ones through to sophisticated testing.

1. DIY Observations

Equipment required: Clear container, flashlight.

  •  Fill a transparent container with water.
  • Shine a flashlight through the water and observe for clarity.

Simple DIY methods involve observing water clarity using basic household items. Fill a clear container with water and shine a flashlight through it. Higher turbidity levels are indicated if the water appears cloudy or particles are visible. It is an indicator that can be seen visually. However, it does not provide accurate readings for turbidity.

2. Home Testing Kits

Equipment required: Turbidity testing kits with instructions.

  •  Follow kit instructions for sample collection and testing.
  •  Kits often include a turbidity meter or test strips for measurements.

Readily available turbidity testing kits come with instructions for sample collection and measurement. These kits usually contain a turbidity meter or test strips. Follow the guidelines to collect a water sample. Perform the test as instructed by the kit. NTU readings often show the accurate results and assess turbidity levels.

3. Professional Labs

Equipment required: Specialized turbidity meters or nephelometers.

  • Collect water samples and send them to certified labs for analysis.
  • Labs employ precise instruments to measure turbidity levels accurately.

Certified laboratories use specialized equipment like turbidity meters for precise analysis. They also apply nephelometers for an accurate analysis. Collect water samples as per lab guidelines and send them for professional testing. The labs have very sensitive meters that take exact reading of the turbidity levels. These devices offer full details of accurate NTU values in their report.

Importance of Testing Turbidity

Regular turbidity testing is vital to:

1. Ensure Water Quality

Turbidity testing serves as a vital tool in assessing water quality by indicating the presence of suspended particles and contaminants. It is essential for various purposes, including drinking, industrial use, and environmental health.

2. Monitor Treatment Effectiveness

Water treatment processes aim to purify water by removing impurities and contaminants. Turbidity testing plays a crucial role in verifying the effectiveness of these treatments.

3. Detect Potential Risks

Variations in turbidity levels can act as an early warning sign for potential health risks associated with water quality. Monitoring turbidity allows for proactive measures to be taken to address these risks before they escalate, safeguarding public health and preventing waterborne illnesses.

4. Comply with Standards

Regulatory bodies often establish safe turbidity levels that must be maintained to ensure water safety and quality. Regular turbidity testing is crucial for ensuring compliance with these standards.

How To Treat Turbidity?

There are multiple ways of treating water turbidity depending on the applications. These measures seek to clarify cloudy waters removing suspended matter. Here’s a comprehensive guide on treating turbidity:

Methods to Treat Turbidity

1. Filtration Systems

Filteration systems are very effective in removing turbidity. They utilise various simple  methods to eliminate turbidity in an efficient way. Here’s how turbidity removal occurs through filtration systems:

Mechanisms of Turbidity Removal:

1. Physical Straining:

  • Mesh or Pore Size: Filters with fine mesh or small pore sizes physically trap suspended particles as water passes through. Larger particles get caught in the filter media, allowing clearer water to flow through.

2. Depth Filtration:

  • Sand, Gravel, or Fabric Filters: Layers of different media, such as sand, gravel, or fabric, create a depth filtration system.

3. Adsorption:

  • Activated Carbon Filters: Activated carbon has a high surface area and can attract particles and impurities to its surface, effectively removing them from the water.

Following systems remove turbidity by filtration:

  1. Mechanical Filters: Use sand, gravel, or fabric to capture particles in water.
  2. Cartridge Filters: Use porous material cartridges to capture particles and offer varying filtration levels.
  3. Multimedia Filters: Combine sand, anthracite, and garnet to enhance filtration efficiency with multiple layers.

2. Coagulation and Flocculation

Coagulation and flocculation are essential processes in water treatment that effectively remove turbidity by causing suspended particles to clump together, facilitating their easier removal. Here’s how this mechanism works:


1. Introduction of Coagulants

Chemical coagulants, such as aluminum sulfate (alum) or polyaluminum chloride, are added to the water. These coagulants create positively charged particles in the water.

2. Neutralizing Charges

These positively charged particles neutralize the negative charges on suspended particles in the water, which typically repel each other, keeping them suspended.

3. Formation of Floc

The neutralized particles begin to come together due to reduced repulsion, forming larger particles known as “floc.”


1. Gentle Agitation

After coagulation, gentle stirring or agitation is applied to the water. This encourages the tiny floc particles to collide and bind together.

2. Formation of Larger Flocs

As the particles collide, they stick to each other, forming larger and heavier flocs.

3. Enhanced Settling

These larger flocs settle more rapidly in the water due to their increased size and weight.

3. Settling and Decanting

Settling and decanting are fundamental processes in water treatment that effectively remove turbidity by allowing suspended particles to settle to the bottom, separating them from the clearer water. Here’s how this mechanism works:


  • Resting Period: After the water undergoes initial treatment or coagulation, it is directed into settling basins or tanks.
  • Gravity-Assisted Settling: The water is allowed to remain still for a certain period. During this time, due to gravity, the suspended particles gradually settle to the bottom of the basin or tank.
  • Particle Separation: Heavier particles settle faster, forming a layer of sediment or sludge at the bottom, while clearer water collects at the top.


  • Careful Removal: Once the settling process is complete, the clearer water at the top, known as the supernatant, is carefully and slowly removed or “decanted” from the settling basin.
  • Avoiding Disturbance: Great care is taken to avoid disturbing the settled particles at the bottom while extracting the clearer water.
  • Leaving Sediment Behind: The sediment containing the settled particles remains undisturbed at the bottom of the basin or tank.

4. Advanced Treatment Methods

Advanced treatment methods are employed to remove turbidity from water through more sophisticated processes that focus on achieving higher levels of purification and clarity. Here’s how advanced treatment methods work to eliminate turbidity:


  • Mechanical or Chemical Processes: Clarifiers are utilized in water treatment plants, employing either mechanical means (like inclined plates or tube settlers) or chemical additives to aid in the settling of suspended particles.
  • Enhanced Particle Settling: The aim is to optimize the settling process by providing conditions that encourage faster and more efficient settling of particles, resulting in clearer water.

Membrane Filtration:

  • Semipermeable Membranes: This method utilizes membranes with extremely fine pores that physically block particles, bacteria, and impurities from passing through.
  • Pressure-Driven Filtration: Water is forced through these membranes, which act as barriers, capturing even the smallest particles and producing exceptionally clear water.

Choosing the Right Treatment Method

  1. Source Water Analysis:
    To determine the best treatment method, understand the turbidity’s nature and composition.
  2. Scale of Treatment:
    When choosing a treatment process, consider the volume of water and available infrastructure.

Steps in Treating Turbidity

1. Pre-Treatment

Remove large particles through screening or sedimentation before employing finer filtration methods.

2. Chemical Treatment

Coagulants are added to promote particle aggregation. This helps remove them through filtration or settling.

3. Filtration

Pass water through different filter media. Capture suspended particles for clearer water.

4. Settling and Clarification

Particles can settle in basins or tanks. Then, separate them using decanting or other methods.

Importance of Treatment

1. Health Protection

Removing suspended particles reduces the presence of pathogens, safeguarding against waterborne diseases.

2. Improved Aesthetics

Enhancing water clarity and eliminating turbidity enhances the visual appeal of drinking water.

3. Efficient Disinfection

Clearer water improves the effectiveness of disinfection processes, ensuring safer drinking water.

Frequently Asked Questions

1. What is the range of turbidity of drinking water?

The safe range for turbidity in drinking water lies between 0.5-1 NTU. Turbidity greater than 1 NTU can negatively affect health.

2. What causes turbidity in drinking water?

Turbidity in drinking water is caused by clay, silt, and organic matter, which prevents proper passage of light.

3. What are the harmful effects of high turbidity?

The harmful effects of high turbidity are:

1. Pathogen Presence
2. Disinfection Challenges
3. Ecological Impact
4. Reduced Water Clarity

4. How to calculate turbidity of water?

Turbidity is measured in Nephelometric Turbidity Units (NTU). The formula for calculating turbidity is Turbidity = (2.3 * A) / L, where A is the absorbance and L is the optical path length.

Bhuwan Bhatia

Bhuwan Bhatia

Bhuwan Bhatia, an engineering graduate with a diverse background, has been passionate about entrepreneurship since age 13. Founder of edtech startup Technoshaala, Bhuwan now focuses on leading his innovative water management startup, FLOTAA, in Kanpur to create sustainable solutions.
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