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Turbidity measures solids in water using the amount of light that can pass through. Turbidity readings can indicate potential pollution and degradation. As turbidity is the measurement of clarity of the water, it is an optical characteristic of water. It is also a measurement of the light that is scattered by material in water.

How Does Turbidity Affect Water Quality?

When a light is shined through a water sample, turbidity is the number of solids that show and indicate quality. The higher the intensity of scattered light, the higher the turbidity.

Turbidity sensors gauge Suspended Solids (SS) in water, typically determining the amount of light passing through the water. Turbidity refers to the clarity of the water, or how clear it is, which determines how much light gets into the water and how far down it goes. Excess soil erosion or dissolved solids can cause turbidity and can block light. Dead plants also increase the organic debris.

What Level of Turbidity is Safe?

The unit of turbidity measurement is called a Nephelometric Turbidity Unit (NTU). The greater the scattering of light, the higher the turbidity. Low turbidity levels and values indicate high water clarity, while high values indicate low water clarity. Turbidity should ideally be kept below 1 NTU because of how it impacts disinfection, as mentioned with drinking water quality.

Turbidity Sensor Water Quality How Turbidity Affects Water

Why is Turbidity Important for Drinking Water Quality?

Although turbid water is not always unhealthy, it can contain particles that humans should not consume. Some problematic particles can include metals or other types of sediment that can have a negative effect on human health.

High turbidity in drinking water acts as a shield for bacteria and other organisms, and as a result, prevents chlorine from disinfecting the water as effectively. Organisms found in water with high turbidity can lead to symptoms like nausea, cramps and headache. Over time, water with high turbidity can even cause staining and clogged pipes, impacting drinking water quality and increasing the risk of illness.

Turbidity and Clarity

Essentially, turbidity measures how cloudy the water is. Water with low turbidity has high clarity, and water with high turbidity has low clarity, indicating water quality. Fine particles like silt, mud, and organic material can reduce water clarity. However, some water bodies naturally have low water clarity. Poor clarity and high turbidity affect aquatic life’s habitat and food supply, such as fish and aquatic birds, and the growth of aquatic plants.


What is the Difference Between Turbidity and Suspended Solids?

Both turbidity and Suspended Solids (SS) are linked and regularly used to measure water and wastewater quality, yet they each have their own specific meaning.


Turbidity refers to the transparency of water. If there are suspended particles in water, this has a direct impact on transparency. High turbidity water will be quite cloudy or murky.

Suspended Solids

SS refers to solid particles that float or drift in the water. For suspended particles to be considered SS, they must be 2microns or larger, with anything smaller being considered a Dissolved Solid (DS). High turbidity water appears cloudy due to SS making the water darker.


Turbidity refers to the transparency of water. If there are suspended particles in water, this has a direct impact on transparency. High turbidity water will be quite cloudy or murky.

The Relationship Between Turbidity Sensors and Water Quality

Turbidity is an important indicator of the number of suspended particles in the water, specifically SS or DS, that can negatively affect aquatic life. The suspended particles that cause turbidity can block light to our aquatic plants, smother other organisms, and carry contaminants like lead, mercury and bacteria.

As turbidity is caused by particles suspended or dissolved in water, particulate matter can include sediment like clay, fine organic and inorganic matter, algae and other microscopic organisms. Such particles can threaten aquatic life and native species and be hazardous to human health should we consume or swim in the water body.

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The RiverWatch blog is the data centre for New Zealanders committed to monitoring and enhancing our waterways. Learn more about the water quality of New Zealand and our integral connection with the waters, and stay up to date with important news, research and developments.