Assessing Water Quality with Total Organic Content

water quality assessment

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Methods for checking water quality are incredibly important as part of the many processes involved in ensuring access to safe drinking water. However, contaminants come from various sources and so it can be difficult to find a generic solution for identifying and removing contamination.

The purification processes for water treatment include removing undesirable bacteria, chemicals, gases and solid waste. This can be very costly. Between 2013 and 2014, utility companies in Wales and England invested £2.1 billion into infrastructure and assorted costs to ensure safe drinking water.1

The analysis of the organic carbon (TOC) content is one of the most broadly used measures for assessing whether water is safe for consumption or not. Dissolved organic carbon content is a measurement of the amount of carbon found in the water as part of organic compounds. This is as opposed to inorganic sources such as carbonic acid salts and carbon dioxide.2 Since the 1970s, it has been a popular approach for both the assessment of drinking water and checking whether wastewater has been sufficiently purified.

The proportion of organic carbon in water is a good proxy for water quality. This because high organic carbon levels indicate either contamination by organic compounds like insecticides and herbicides, or a high level of organisms in the water. High levels of microorganisms can arise for various reasons but are often a sign of contamination from a source of wastewater.

Testing TOC

To check water is safe for consumption, it needs to be monitored continually for signs of change in the TOC. Although many countries do not specifically regulate for TOC levels, the concentrations of specific volatile organic compounds are covered by legislation. Recommended levels of TOC are 0.05 ml/l or less.3

There are various approaches for testing water for organic carbon. One approach is to measure the entire carbon content (inorganic and organic) and then subtract any carbon dioxide detected (as this is considered inorganic carbon) as well as any other carbon from inorganic sources. Another approach uses chemical oxidation or high temperature so that all the organic compounds in the sample will be oxidized to carbon dioxide. Therefore, measuring the carbon dioxide levels acts as a proxy for the TOC concentration.

Being able to perform online, real-time analysis of water content is key for water measurement plants. Measurements need to be accurate and sensitive enough to detect small changes in even low concentrations of chemical species. Under UK law, it is an offense to supply drinking water that does not comply with legislation4. Suppliers are fined over £300,000 for providing drinking water that is contaminated.5

Vigilant Monitors

Carbon dioxide absorbs infrared light very strongly and this is one of the advantages of using carbon dioxide levels as a proxy for TOC. Therefore, using non-dispersive infrared (NDIR) detectors provides a very sensitive way of detecting carbon dioxide, even in trace amounts.

Edinburgh Sensors are one of the world leaders in NDIR sensor production, offering a variety of NDIR-based gas detectors that are suitable for TOC water measurements.6 For quick, reliable and easy TOC measurements, the Gascard NG is an excellent device for quantifying the levels of carbon dioxide.7

Gascard NG

The Gascard NG is well-suited to continual carbon dioxide monitoring for various reasons. Firstly, it can detect a wide variety of carbon dioxide concentrations, ranging from 0 to 5000 ppm, while maintaining accuracy of ± 2% over the complete detection range. This is important to ensure that the sensor is sensitive enough to check that TOC levels are low enough to be safe for drinking water. It also means that it can operate under conditions where TOC levels may be very high, for example, in wastewater purification processes.

The Gascard NG can come with built-in true RS232 communications for control and data logging means that it can be used to constantly monitor carbon dioxide levels as well as be integrated into feedback systems such as for water purification. This enables it to change treatment approaches if the TOC content becomes too high. UK legislation requires a certain level of record-keeping for water quality levels and this can be easily automated with the Gascard.4

Gascard NG

Gascard NG. Image Credit: Edinburgh Sensors

The Gascard NG can perform self-correcting measurements over a range of humidity conditions (0 – 95%) and these readings can be pressure-corrected with on-board electronics between 800 and 1150 mbar. To ensure reliable measurements over a wide range of environmental conditions, the Gascard NG also features temperature compensation between 0 and 45 oC.

The Gascard NG is designed to be fail-safe, robust and maintenance-free. It comes with several customizable options. The expansion port can be used for small graphical display modules for in-situ observable readings. If communications over standard networks are required, TCP/IP communications can also be included. This means that when used in conjunction with Edinburgh Sensor’s expertise and pre- and post-sales support, the Gascard NG can be integrated into existing TOC measurement systems to ensure fast and accurate monitoring at all times.

References and Further Reading

  1. Water and Treated Water (2019),
  2. Volk, C., Wood, L., Johnson, B., Robinson, J., Zhu, H. W., & Kaplan, L. (2002). Monitoring dissolved organic carbon in surface and drinking waters. Journal of Environmental Monitoring, 4(1), 43–47.
  3. DEFRA (2019)
  4. Water Legislation (2019),
  5. United Companies Contamination (2019) Sensors (2019),
  6. Gascard NG, (2019),

This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.

For more information on this source, please visit Edinburgh Sensors.


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