Oxidation-Reduction Potential (ORP) is a measure of the water’s ability to either oxidise or reduce another substance. A positive ORP reading indicates that the substance is an oxidising agent and a negative reading is indicative of a reducing agent being present.
ORP is centred around the exchange of electrons between substances as an oxidising agent will take electrons from other molecules, by contrast, reducing agents will tend to give up electrons to other molecules.
ORP belongs to the ‘classic’ suite of physicochemical tests for water quality as an indicator of cleanliness of the tested water.
High ORP indicates that there is a high proportion of oxidising agents present as the solution has a higher electronegativity. Oxidising agents will take electrons from other substances such as bacteria or contaminants present in the water.
As an ‘at-a-glance’ measure, ORP is a good indicator of the sanitation level of the water and its ability to ‘clean’ itself. Elements such as oxygen and chlorine will substantially increase ORP, hence why Chlorination is a well-known treatment method.
Environmental waters such as lakes need the ability to ‘clean’ themselves of contaminants that enter the system, for example deceased plant and animal matter.
ORP is unfortunately not infallible as it is susceptible to the presence of other dissolved ions as well as the presence of total dissolved solids which will not be contributing to sanitation but could have an impact on the reading.
ORP is a good instant assessor of water quality and can pick up on warning signs that there is a drop in water quality. It is often used in-conjunction with Dissolved Oxygen (DO) as it can provide additional context as to the degree of pollution and overall system health.
ORP is measured in a similar method to pH using electrodes but instead of hydrogen ions, it measures electron activity in the water and compares to a reference electrode solution.
The Proteus measures ORP using a platinum sensor which can be attached to the pH sensor.
The output is in millivolts (mV).
