Spectrophotometers, Colorimeters and Turbidity meters are all optical measurement systems that are critical for determining concentrations of specific analytes or other attributes of aqueous samples.

All three categories of optical instruments are frequently key parts to a laboratory’s analytical suite and called upon to support water quality compliance programs.

light measurement

Spectrophotometric and colorimetric measurements use a light source to pass a narrow band of light straight through a reacted test sample in a vial. The light beam exiting the sample vial is collected in a detector in-line with the initial beam. The associated value is then converted to a concentration for that specific analyte. Some single parameter colorimeters perform one specific analyte measurement. Multi-parameter meters can do many tests and require the user to select the appropriate method to match the test and reagent type being used for the analyte of interest.

These tests allow you to expand your testing capabilities for many species, including those that are not detectable by pH, DO, Conductivity and Ion Selective Electrode (ISE) electrochemical methods. Many if not most determinations using spectrophotometers and colorimeters require the use of a reagents. These reagents will react with the targeted component of the sample. The user can then measure the reacted sample in their colorimeter to determine the concentration of the component in that sample. The sample result is compared to a programmed curve in the meter of reacted, known standard values. The concentration measurement can be seen on the display.

Globally, there are many regulations that are in place to ensure our drinking water is safe to drink and our wastewater will not pollute, alter, or destroy our local water resources and oceans. Regulations vary according to water use. For example, a disinfectant used to kill pathogens is commonly tested by a colorimeter, such as an Orion AQUAfast Colorimeter. Similarly, water that is used as a drinking water supply may need to be regularly checked to ensure that it is free of chemical contaminants.

Many test reagents are available for measuring parameters that are reported as required on regulatory compliance permits.

Identifying turbidity levels in "cloudy" samples

Turbidity is a measurement of “cloudiness” or the effect of particulates dispersed in a sample. The more particles present, the higher the sample’s turbidity. Since turbidity can be a visually subjective attribute, an instrument is needed to quantify how turbid a sample is. Turbidity meters, sometimes referred to as “nephelometers” evaluate light scatter in samples, using a light source and a detector at a 90 degree angle. Then they assign a numerical value to the level of turbidity in a sample. It should be noted that turbidity meters require standards to calibrate the meter periodically and to check the calibration. The Orion AQ4500 Method, based on the AQUAfast AQ4500 Turbidimeter is U.S. EPA approved for drinking water and wastewater reporting and satisfies the ISO 7027 measurement requirements with our ISO Nephelometric mode. The Orion AQUAfast AQ3010 turbidity meter also complies with ISO 7027 requirements.


Vis and UV-Vis Spectrophotometers are powerful analytical instruments that can be used with preprogrammed methods or with user defined concentration curves to determine the concentration of a target analyte in a substance.

Colorimeters are similar to spectrophotometers in the they can utilize pre-programmed methods, some also have the ability for the user to create custom methods as well but because they have simplified optical systems and a limited selection of light frequencies they tend to be used as cost effective / portable analytical instruments.

Turbidity meters are unique instruments that determine how cloudy and particulate-laden the sample is and report a numeric value for turbidity 

Water Quality Resource Library

resource-libraryVisit our Water Quality Resource Library to review the colorimetry and turbidity manuals and instruction sheets. You will find our U.S. EPA approved Orion AQ4500 Drinking Water and Wastewater turbidity methods. Our spectrophotometers, colorimeters, and turbidity meters are being used around the world to meet regulatory compliance testing method requirements. We have posted many application notes and briefs to assist you with your testing.
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