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An inline sensor for recycled water cross-connections


Impact theme: More about impact themes
Technology and Treatment


Recycled water is now commonly supplied to properties using a dual reticulation system with two sets of pipes—one for drinking water, and one for recycled water used for flushing toilets and outdoor uses. Cross-connections, misconnections and water system faults occasionally cause the two supplies to mix, impacting drinking water quality. Early-warning technology to support smart water metering at individual premises would improve safety and increase public confidence in these third-pipe schemes. This project aims to develop an automated sensor that measures water quality in pipes (or ‘inline’) in real-time by testing both ultraviolet (UV) absorbance and fluorescence and immediately warn of such mixing. The project aimed to reliably detect as little as 10 per cent contamination of potable water with recycled water. A paired sensor was developed in the form of an inline sensor that measures electrical conductivity to enhance the detection of contamination of potable water with recycled water, using existing CSIRO technology.


Work undertaken and outcomes

UV fluorescence was found to offer superior sensitivity when compared to UV absorbance, and offered improved affordability for detection of cross-connections. Operational prototypes were developed with a component cost under AU$200. The final prototype was able to detect under 3% recycled water in a potable water in the laboratory. A test rig, incorporating a paired fluorescence sensor and an electrical conductivity (EC) sensor was demonstrated to work effectively in two field trials conducted on varying water quality types at Brushy Creek (Yarra Valley Water) and Surbiton Park (Western Water).

The fluorescence prototype has been demonstrated to provide an excellent means of differentiating water quality over long periods of time at low cost. The opportunity exists to develop a cross connections device based on changes in fluorescence and EC properties of recycled water for use within consumer premises. The fluorescence sensors did not experience any catastrophic failures or problems associated with biofouling.The total cost of the components for the prototype device costs would be expected to be further reduced with production scaling.


Adoption and impact


To support continuing commercial development, the Centre has provided an additional $20,000 to CSIRO to conduct a further pilot of the fluorescence sensors and electrical conductivity sensors to detect cross-connections between potable and recycled water at City West Water’s (CWW) Werribee Scheme, Victoria.  The CSIRO and CWW have signed a Research Agreement for this project and are currently developing a plan for the deployment of sensors and to investigate the best configuration of fluorescence and electrical conductivity sensors. Further information on this project is available from the project leader, Dr Tim Muster.



Michael Best, CSIRO, undertaking water quality measurements with four inline flourescence sensor prototypes



Field unit to test the ability to detect cross-connections being assembled


Project Partners

Lead organisation: Commonwealth Scientific and Industrial Research Organisation (CSIRO) Land and Water Flagship
Partner organisations: Smart Water Fund
Melbourne Water
Yarra Valley Water
Western Water
Hawk Measurement Systems


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