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Water Quality Measurement

Monitoring low or no chlorine residuals in your reticulation network.

The current situation

Many Utilities around Australia have vast reticulation networks that may have very few customers connected to them but are still required to provide a chlorine residual as per the Australian Drinking Guidelines (v3.5 August 2018). Measuring low levels of chlorine residual can be difficult with online analysers and handheld DPD meters as the limit of detection is typically 0.04mg/L. Online analysers tend to depolarize and lose calibration with consistent low-level residuals below 0.05mg/L.

So how do we measure low/no residuals in the reticulation network with a stable sensor suited to these conditions?

ORP Measurement

An Oxidation Reduction Potential (ORP) Probe can be used to measure low chlorine residuals, as the probe is looking for the oxidizing power of the disinfecting agent in the water, the ORP probe can be used to provide a surrogate measurement of other chemicals such as chlorine/monochloramine or ozone. The ORP probes do not depolarize like membrane chlorine sensors, making them the sensor of choice for low or no residual monitoring.

So, what does an ORP probe measure?

ORP can be used to determine the efficacy of chemical disinfectants that work via the oxidation or reduction of the structures of microbial contaminants. For example, chlorine, an oxidant, will strip electrons from the negatively charged cell walls of some bacteria. Because ORP measures the total chemical activity of a solution, ORP measures the total efficacy all oxidizing and reducing disinfectants in solution: Hypochlorous acid, monochloramine, dichloramine, hypobromous acid, sodium hypochlorite, UV, ozone, peracetic acid, bromochlorodimethylhydantoin, etc.

ORP indicates the effectiveness of only those disinfectants that work through oxidation and reduction. ORP cannot be used to detect the presence of any one particular chemical or chemical species. Nor can it alone be used to determine the concentration of a known species of chemical in solution. This means that although ORP is the best way to know whether or not your sanitizer is working, it can’t tell you how much or what kind of sanitizer is working.

The Solution

With the introduction of the Clamnet (Metrinet) online battery powered 4G water quality monitoring system in 2020. We now have the option to measure up to 8 sensor parameters or just one single parameter like ORP.

The Clamnet system can be mounted in a Pelican case or other enclosure to provide a lift and shift or fixed monitoring solution to determine if you have any type of disinfection in remote parts of your reticulation network.

If you’re interested in finding out more about our Water Quality Measurement solutions and how it can benefit your operations, contact our Smart Utilities Product Manager, Adam Simpson or get in touch with the SGA team today!


The above explanation of ORP measurement was from Heather Rekalske in her article Making the case for ORP on the watertechonline website. The full article can be found here.

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