Do you like your water sparkling and crystal clear? Water’s clarity and transparency are good clues for its turbidity level. For safe drinking water, turbidity should not exceed 5 NTU.
But what really is turbidity and how do you measure it? This blog will help you understand turbidity and its importance in drinking water.
What is Turbidity?
Turbidity is an optical characteristic of water. It measures its relative clarity. When water appears murky, it is a sign of high turbidity.
Turbidity is simply a measure of cloudiness or haziness of water. High levels of suspended particles equals higher turbidity. It is measured in nephelometric turbidity units (NTU).
Suspended materials like clay, silt, scatter and disperse light. Their presence increases turbidity levels as water with such contaminants gets opaque.
Other materials include inorganic and organic matter, algae, plankton, and other microscopic organisms.
Factors Affecting Water Turbidity
- Natural Events like heavy rainfall and flooding stir up sediments.
- Man-made pollution, land erosion, and agricultural runoff contribute to turbidity.
- Industrial chemicals and pollutants from wastewater can increase turbidity.
- Construction sites and deforestation can lead to soil erosion and increased turbidity.
- Algae growth blocks sunlight from reaching the water column.
- Animals can increase turbidity by stirring up silt or releasing waste into the water.
Why Is Turbidity Important In Water Quality?
High turbidity levels can reflect potential health risks and pollution levels. Controlling turbidity levels safeguards public health and maintains healthy ecosystems.
Turbidity vs. Total Suspended Solids (TSS)
Turbidity and Total Suspended Solids (TSS) are both related to suspended particles.
Turbidity measures the cloudiness of water (NTU). In contrast, TSS measures the concentration of suspended particles (mg/L).
Turbidity is more sensitive to smaller particles. TSS is more sensitive to larger ones.
Common Suspended Solids in Water
Bacteria
Bacteria, like Legionella and Coliforms, are common in well water. Some bacteria can make you sick, while others suggest harmful bacteria might be in the water.
Clay
Clay, especially colloidal clay, is often found in well water. It can make water cloudy. While not usually harmful in small amounts, clay can affect the taste and smell of water and is hard to remove.
Gravel
Gravel particles make water look dull or cloudy, but they’re too small to see with the naked eye. Gravel settles at the bottom because it’s heavy.
Sand
Sand is a problem in areas with sandy soil, especially in well water. It’s heavier and settles at the bottom, but can be filtered out with a sediment filter.
Silt
Silt is between the size of sand and clay. It’s found in rivers, lakes, and soil. While not dangerous, silt can make water look unattractive.
How Is Turbidity Measured In Drinking Water?
Low turbidity reflects the absence of harmful pathogens and contaminants.
Use a turbidimeter for accurate measurement. Take at least two readings to meet calibration standards and ensure accuracy. Nephelometers (turbidity meters) can be used as well.
Turbidity is measured in either NTU (Nephelometric Turbidity Units) or FTU (Formazin Turbidity Units).
In developed countries, drinking water should have a turbidity level below 1 NTU. Many water companies aim for even lower levels: ~0.2 NTU.
Developing countries should maintain turbidity levels below 5 NTU to ensure safety.
High turbidity levels signal inadequate treatment processes and compromised filtration systems. Turbidity should be measured periodically to maintain water quality standards.
Turbidity also reveals the presence of solids that may precipitate and affect flavor. For example, calcium can give water and beverages a bitter taste.
Why Is Turbidity Important To Organisms Like Fish?
In streams and lakes, increased sedimentation and siltation occur from rainfall and erosion. High turbidity harms fish habitats and other aquatic ecosystems.
High turbidity (>100,000 NTU) can kill fish and negatively affect aquatic ecosystems:
- Turbidity can limit visual cues for fish movement, hindering their migration.
- Sediment can affect fish gills, leading to respiratory issues and reduced health.
- Turbidity can block sunlight, limiting photosynthesis and reducing oxygen levels.
- Reduced plant food and oxygen can affect predator-prey dynamics and biodiversity.
Turbidity Measurement Techniques
Turbidimeters and nephelometers measure turbidity by detecting scattered light from suspended particles.
Nephelometers provide high sensitivity to low turbidity levels, ideal for laboratory settings.
For a cost-effective alternative, turbidity tubes allow for visual assessment of turbidity levels. They are useful for field measurements, though less precise than electronic devices.
Selecting the Right Instrument
When choosing a turbidity instrument, consider:
Range: Determine the required turbidity range (low or high).
Particle Sensitivity: Consider the specific particles you need to measure (clay, silt, algae).
Ease of Use: Opt for instruments that are user-friendly and require minimal training.
Cost: Factor in the initial cost and long-term expenses for maintenance and calibration.
Types of Turbidity Instruments:
- Nephelometers measure light scattered at 90 degrees, ideal for low turbidity.
- Turbidimeters measure the intensity of light transmitted through water, influenced by particles.
- Ratio and Nephelometric Turbidimeters measure transmitted and scattered light for precise turbidity measurement.
Ensuring Regulatory Compliance
The EPA sets strict turbidity standards for drinking water, wastewater, and surface water in the US:
- Drinking Water: The average maximum annual turbidity must not exceed 0.3 NTU.
- Wastewater Discharge: Maximum turbidity for wastewater discharged into surface water is 30 NTU.
- Surface Water: 10 NTU (max) is allowed to protect aquatic habitats.
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Frequently Asked Questions
How Does Turbidity Impact Swimming?
High turbidity reduces visibility and poses safety risks for swimmers.
What Are the Health Risks of High Turbidity?
High turbidity may increase waterborne pathogens and reduce filtration effectiveness.
Can Turbidity Be Natural?
Turbidity can occur naturally. Natural events include rainwater flooding, animals, and water pollution. Aquatic plants combat turbidity by absorbing nutrients and reducing suspended particles.
