Dissolved Oxygen (DO) refers to the amount of gaseous oxygen that a water system contains. DO arises primarily from two main processes: photosynthesis and diffusion from the atmosphere. Agitated water systems will dissolve more oxygen through diffusion, therefore flowing and tidal water systems are expected to have higher DO concentrations than stagnant or quiescent waters. Many environmental factors influence how much DO water can contain. Temperature, salinity, and altitude are just some of the natural factors that can limit the DO concentration. Dramatic and unexpected decreases in DO concentration typically result from contamination of the water source. The most common contaminants are bacteria and organic matter. Nutrient run-off from fertilizers is also a major source of contamination that can dramatically reduce DO in water. From this, it is evident that DO can be an indicator of the overall health of the water system. A decrease in DO or the presence of pollutants becomes apparent quickly in river and lake waters, due to eutrophication. For potable water, however, this is not as readily apparent. Therefore, it is necessary to actively monitor drinking water systems to ensure that the water is safe to consume. Regular monitoring of DO in drinking water can establish a baseline of normal "healthy" conditions. Significant deviations from this normal conditions can therefore indicate an issue, most likely due to contamination. Current approaches to DO sensing are based on optical or electrochemical detection mechanisms, both of which can be undertaken at a point-of-interest. Optical based DO sensors typically operate by measurement of the luminescence response of a molecule in the presence of oxygen, where oxygen typically quenches the luminescence. Higher concentrations of oxygen mean less luminescence, so a quantitative measure can be obtained. The luminescent species, typically an organic molecule, is provided as part of the overall device, simplifying the analysis. A drawback, however, is that luminescent species needs to be replenished over time and can be influenced by environmental factors, such as temperature, selfquenching and pH. Electrochemical approaches to DO sensing, typically involve measurement by direct reduction of oxygen at an electrode surface. The reaction that governs this is shown in Eq. 1. 𝑂 2 + 4𝐻 + + 4𝑒 -→ 2𝐻 2 𝑂 Eq. 1