OTT HydroMet

Quality assurance and Quality control technical note

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Courtesy of OTT HydroMet


For almost 50 years HYDROLAB products have provided dependable sensor technology in a multiple parameter instrument for montioring essential indicators required for assessing water quality in natural waters. Useable data are the lifeblood of any environmental water quality monitoring program and variation in measurement processes impairs the quality of the data that water resource professionals work so hard to obtain. Differences in operators, equipment calibration procedures, test methods, environmental conditions, and other factors can contribute to discrepancies between measurement results – whether comparisons are from time to time, site to site, instrument to instrument, or operator to operator. The primary activities taken to assure and control data quality are aptly called quality assurance and quality control. Quality assurance (QA) refers to planned and systematic processes that provide confidence in a measurement process’ ability to achieve its intended outcome. Examples of QA activities include methodology development and 

standards validation. Quality control (QC) activities, such as testing and inspection, aim to find defects in specific elements of the measurement process. The differences between QA and QC activities can be subtle, which is why they are often seen combined as simply “QA/QC.”

The 'True Value'
Determining the 'true value' of a water quality measurement is an important fundamental of any QA/QC program. To determine the true value, many professionals apply a second means of measuring the parameter of interest, such as another instrument that is kept serviced and calibrated just for quality control purposes or a grab sample that is evaluated using a trusted laboratory technique.

The true value used in a QA/QC program is a surrogate - a value very close to the true value and accepted as such. This surrogate true value is sometimes referred to as an assigned value, accepted value, or reference value. Calibration standards may also be used as a reference value. Good QA/QC programs require robust calibration procedures that ultimately provide valuable information about, and confidence in, the instrument's performance. The following section highlights key information made available during a HYDROLAB multi-parameter water quality sonde calibration.

HYDROLAB Operating System for use with HL Series Sondes decisions, minimize errors, and increase efficiency in the lab and on the deployment site.

The HYDROLAB Operating System is a powerful software tool that helps to make better decisions, minimize errors, and increase efficiency in the lab and on the deployment site.

Calibration Process

  • Calibrate sensors and check sensor calibrations with guided and semiautomated calibration routines
  • Access and create metadata that give system information, calibration history, user information, and site information

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