EPA-NERL: 180.1:  Turbidity by Turbidimeter

  • Summary
  • Analytes
  • Revisions
  • Data and Sites
Official Method Name
Determination of Turbidity by Nephelometry
Current Revision
Revision 2.0, August 1993
Method Subcategory
Method Source
  Methods for the Determination of Inorganic Substances in Environmental Samples (EPA/600/R-93/100)
Brief Method Summary
The method is based upon a comparison of the intensity of light scattered by the sample under defined conditions with the intensity of light scattered by a standard reference suspension. The higher the intensity of scattered light, the higher the turbidity. Readings, in NTU's, are made in a nephelometer designed according to specifications outlined in the method. A standard suspension (i.e., formazin, AMCO-AEPA-1, or Hach Stablcal) is used to calibrate the instrument.
Scope and Application
This method is applicable to drinking, surface, and saline waters in the range of turbidity from 0 to 40 nephelometric turbidity units (NTU). Higher values may be obtained with dilution of the sample.
Applicable Concentration Range
0 - 40 NTU
The presence of floating debris and coarse sediments which settle out rapidly will give low readings. Finely divided air bubbles will affect the results in a positive manner. The presence of true color, that is the color of water which is due to dissolved substances which absorb light, will cause turbidities to be low, although this effect is generally not significant with finished waters.
Quality Control Requirements
Sample Handling
Preservation of the sample is not practical; analysis should begin as soon as possible. Refrigeration or icing to 4oC, to minimize microbiological decomposition of solids, is recommended.
Maximum Holding Time
48 hours (MCAWW, Table I)
Relative Cost
Less than $50
Sample Preparation Methods