ASTM D6855 - 12

    Standard Test Method for Determination of Turbidity Below 5 NTU in Static Mode

    Active Standard ASTM D6855 | Developed by Subcommittee: D19.07

    Book of Standards Volume: 11.01


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    Significance and Use

    Turbidity is undesirable in drinking water, plant effluent waters, water for food and beverage processing, and for a large number of other water-dependent manufacturing processes. Removal is often accomplished by coagulation, settling, and filtration. Measurement of turbidity provides a rapid means of process control for when, how, and to what extent the water must be treated to meet specifications.

    This test method is suitable to turbidity such as that found in drinking water, process water, and high purity industrial water.

    When reporting the measured result, appropriate units should also be reported. The units are reflective of the technology used to generate the result, and if necessary, provide more adequate comparison to historical data sets.

    Table 1 describes technologies and reporting results (see also Refs (1),(2),(3)). Those technologies listed are appropriate for the range of measurement prescribed in this method. Others may come available in the future. Fig. X5.1 provides a flow chart to aid in selection of the appropriate technology for low-level static turbidity applications.

    If a design that falls outside of the criteria listed in Table 1 is used, the turbidity should be reported in turbidity units (TU) with a subscripted wavelength value to characterize the light source that was used.

    TABLE 1 Applicable Technologies Available for Performing Static Turbidity Measurements Below 5 NTU

    Design and
    Reporting Unit
    Prominent ApplicationKey Design FeaturesTypical Instrument RangeSuggested Application
    Nephelometric
    non-ratio (NTU)
    White light turbidimeters. Comply
    with USEPA Method 180.1 (1)
    for low level turbidity monitoring.
    Detector centered at 90° relative
    to the incident light beam. Uses
    a white light spectral source.
    0.020 to 40Regulatory reporting
    of clean water
    Ratio White Light
    turbidimeters (NTRU)
    Complies with ISWTR regulations and
    Standard Method 2130B. (2)
    Can be used for both
    low and high level
    measurement.
    Used a white light spectral source.
    Primary detector centered at 90°.
    Other detectors located at other angles.
    An instrument algorithm uses a
    combination of detector readings to
    generate the turbidity reading.
    0.020 to10 000Regulatory Reporting of
    clean water
    Nephelometric, near-IR
    turbidimeters,
    non-ratiometric (FNU)
    Complies with ISO 7027.
    The wavelength is less susceptible
    to color interferences.
    Applicable for samples with color
    and good for low level monitoring.
    Detector centered at 90° relative to
    the incident light beam. Uses a near-IR
    (780-900 nm) monochromatic light source.
    0.012 to 10000 - 40 ISO 7027
    Regulatory reporting
    Nephelometric near-IR
    turbidimeters,
    ratio metric (FNRU)
    Complies with ISO 7027. Applicable
    for samples with high levels
    of color and for monitoring
    to high turbidity levels.
    Uses a near-IR monochromatic light
    source (780-900 nm). Primary detector
    centered at 90°. Other detectors located
    at other angles. An instrument algorithm
    uses a combination of detector readings
    to generate the turbidity reading.
    0.012 to 10 0000 - 40 ISO 7027
    Regulatory reporting
    Nephelometric Turbidity
    Multibeam Unit (NTMU)
    Is applicable to EPA regulatory
    method GLI Method 2. (2)
    Applicable to drinking water
    and wastewater monitoring applications.
    Detectors are geometrically centered at
    0 and 90°. An instrument algorithm uses
    a combination of detector readings,
    which may differ for turbidities
    varying magnitude.
    0.012 to 40000 to 40 Reporting for
    EPA and ISO compliance
    mNTUIs applicable to reporting of clean
    waters and filter performance
    monitoring. Very sensitive to
    turbidity changes in low
    turbidity samples. (3)
    Nephelometric method involving a
    laser-based light source at 660-nm and
    a high sensitivity photo-multplier tube
    (PMT) detector for light scattered at 90°.
    1000 mNTU = 1 NTU
    5 to 5000 mNTU or
    0.005 to 5.000 NTU
    0-5000 mNTU, for EPA
    compliance reporting on
    drinking water systems

    1. Scope

    1.1 This test method covers the static determination of turbidity in water (see 4.1).

    1.2 This test method is applicable to the measurement of turbidities under 5.0 nephelometric turbidity units (NTU).

    1.3 This test method was tested on municipal drinking water, ultra-pure water and low turbidity samples. It is the user's responsibility to ensure the validity of this test method for waters of untested matrices.

    1.4 This test method uses calibration standards are defined in NTU values, but other assigned turbidity units are assumed to be equivalent.

    1.5 This test method assigns traceable reporting units to the type of respective technology that was used to perform the measurement. Units are numerically equivalent with respect to the calibration standard. For example, a 1.0 NTU formazin standard is also equal to a 1.0 FNU standard, a 1.0 FNRU standard and so forth.

    1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Refer to the MSDSs for all chemicals used in this procedure.


    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    D1129 Terminology Relating to Water

    D1192 Guide for Equipment for Sampling Water and Steam in Closed Conduits

    D1193 Specification for Reagent Water

    D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water

    D3370 Practices for Sampling Water from Closed Conduits

    D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis

    E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

    Other Referenced Standards

    ISO7027 (The International Organization for Standardization) Water Quality--for the Determination of Turbidity Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036.


    ICS Code

    ICS Number Code 19.100 (Non-destructive testing)

    UNSPSC Code

    UNSPSC Code


    Referencing This Standard

    DOI: 10.1520/D6855-12

    ASTM International is a member of CrossRef.

    Citation Format

    ASTM D6855-12, Standard Test Method for Determination of Turbidity Below 5 NTU in Static Mode, ASTM International, West Conshohocken, PA, 2012, www.astm.org

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