ASTM D7726-11(2016)e1
Standard Guide for The Use of Various Turbidimeter Technologies for Measurement of Turbidity in Water

Standard No.

ASTM D7726-11(2016)e1

Release Date

2011

Published By

American Society for Testing and Materials (ASTM)

Status

Be replaced

Replace By

ASTM D7726-11(2023)

Latest

ASTM D7726-11(2023)

Scope

5.1 Turbidity is a measure of scattered light that results from the interaction between a beam of light and particulate material in a liquid sample. Particulate material is typically undesirable in water from a health perspective and its removal is often required when the water is intended for consumption. Thus, turbidity has been used as a key indicator for water quality to assess the health and quality of environmental water sources. Higher turbidity values are typically associated with poorer water quality.

5.1.1 Turbidity is also used in environmental monitoring to assess the health and stability of water-based ecosystems such as in lakes, rivers and streams. In general, the lower the turbidity, the healthier the ecosystem.

5.2 Turbidity measurement is a qualitative parameter for water but its traceability to a primary light scatter standard allows the measurement to be applied as a quantitative measurement. When used as a quantative measurement, turbidity is typically reported generically in turbidity units (TUs).

5.2.1 Turbidity measurements are based on the instruments’ calibration with primary standard reference materials. These reference standards are traceable to formazin concentrate (normally at a value of 4000 TU). The reference concentrate is linearly diluted to provide calibration standard values. Alternative standard reference materials, such as SDVB co-polymer or stabilized formazin, are manufactured to match the formazin polymer dilutions and provide highly consistent and stable values for which to calibrate turbidity sensors.

5.2.1.1 When used for regulatory compliance reporting, specific turbidity calibration standards may be required. The user of this guide should check with regulatory entities regarding specifics of allowable calibration standard materials.

5.2.2 The traceability to calibrations from different technologies (and other calibration standards) to primary formazin standards provides for a basis for defined turbidity units. This provides equivalence in the magnitude of the turbidity unit between the different measurement technologies when they are all calibrated on standards that are traced to primary formazin. This means that a TU is equivalent in its magnitude to a nephelometric turbidity unit (NTU), and all other units as described in this guide. See Table 1.

5.2.3 Turbidity is not an inherent property of the sample, such as temperature, but in part is dependent on the technology used to derive the value. Even though the magnitude of turbidity units are equivalent and are based on turbidity standards, the units do not maintain this equivalence when measurement of samples is practiced. Turbidity standards are generally free of interferences and samples are not. Depending on the type of technology employed for measurement, the magnitude of the different interferences on a given sample can differ significantly with respect to the different measurement technologies. The user of a turbidity technology should expect to observe a lack of measurement equivalence across different turbidity measurement designs when common samples are analyzed. See Section 6 on interferences.

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ASTM D7726-11(2016)e1 Referenced Document

• ASTM D1129 Standard Terminology Relating to Water
• ASTM D3977 Standard Test Methods for Determining Sediment Concentration in Water Samples
• ASTM D6698 Standard Test Method for On-Line Measurement of Turbidity Below 5 NTU in Water*， 2024-04-20 Update
• ASTM D6855 Standard Test Method for Determination of Turbidity Below 5 NTU in Static Mode
• ASTM D7315 Standard Test Method for Determination of Turbidity Above 1 Turbidity Unit (TU) in Static Mode

ASTM D7726-11(2016)e1 history

• 2023 ASTM D7726-11(2023) Standard Guide for The Use of Various Turbidimeter Technologies for Measurement of Turbidity in Water
• 2011 ASTM D7726-11(2016)e1 Standard Guide for The Use of Various Turbidimeter Technologies for Measurement of Turbidity in Water
• 2011 ASTM D7726-11 Standard Guide for The Use of Various Turbidimeter Technologies for Measurement of Turbidity in Water