What is Turbidity?
Turbidity is haze or cloudiness in water caused by suspended and colloidal particles or matter. Turbid water is commonly described as hazy, milky, cloudy or dirty. High levels of turbidity usually indicate low water quality. Turbidity can vary from a muddy river or pool (high turbidity) to a clear stream (low turbidity). Suspended/colloidal particles are typically picked up in streams and rivers, and are composed of clay, silt, dirt, organic debris, lime scale and corrosion/oxidation products (rust, lead, copper oxides etc).
Although turbidity is not intrinsically harmful, it can shield harmful contaminants (e.g. viri or bacteria) from disinfectants such as chlorine. Turbidity particles can also absorb and carry other dissolved contaminants throughout a water supply system. High turbidity can block filters and fill pipes and tanks with mud and silt and cause damage to valves and taps. Turbidity also is undesirable for aesthetic reasons and texture in potable water and consumer products.
One the primary applications for turbidity reduction and monitoring is in drinking water supplies. Cross flow membranes, including reverse osmosis, nano-filtration or ultra-filtration, are commonly used to remove or reduce turbidity.
A common field test to check for turbidity is to hold a torch up to a water sample. If the light makes the sample look cloudy or the beam highlights particles in the water, your sample is turbid.
Turbidity levels can be more accurately quantified using either a turbidimeter or nephelometer. Turbidimetry measures the loss of intensity of light transmitted through the sample through the scattering effect of suspended particles and nephelometry measures the intensity of light scattered at 90° relative to the light source, compared to a reference solution. Both methods employ Nephelometric Turbidity Units (NTU).
Colourimetric Water Analysis
Turbidity interferes with instrumental colourimetric water analysis by causing discolouration and light scattering in the sample when measured with a photometer or spectrophotometer, resulting in elevated readings. In order to reduce inaccuracies in sample measurement due to light scattering, the following methods are available.
One option is to reduce the sample turbidity using filtration, however this may not always be appropriate depending on the testing environment or the analyte being measured.
A second option is to perform a sample dilution to the lower end of the range of the available test kit, or use another lower range test kit. However, besides the potential to introduce inaccuracies through improper dilution procedures, the effective kit accuracy is reduced by the factor of the dilution. It also not appropriate for all analytes.
If sample filtration or dilution are not practical or appropriate for your analyte and you do not want to introduce inaccuracies from sample dilution, then the Sample Zeroing Accessory Pack may be your answer. The Sample Zeroing Accessory Packs allow the operator to zero the instrument with a zero blank from the same source as the water sample. This corrects for the turbidity in the sample allowing for a more accurate measurement of the analyte being tested.
- CHEMetrics (2020). Turbidity and the Sample Zeroing Accessory Pack. Retrieved 8 August 2020 from:
- WHO. Fact Sheet 2.33: Turbidity Measurement. Retrieved 8 August 2020 from:
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