What is ORP in solution testing?

You may have heard of ORP, but what does it mean, and what role does it play in water quality testing? We've laid out the basics of ORP to get you started quickly.

Also, in this post, we'll delve into the role of ORP in water pollution, as well as Water Quality 101: pH in Water Testing.

What is Oxidation-Reduction Potential (ORP)?

Oxidation-reduction potential (ORP) is a measure of the ability of one substance to oxidize or reduce another. It is measured by the electrodes of the ORP meter. A positive reading on the ORP meter indicates that the substance is an oxidizing agent; a negative reading indicates that the substance is a reducing agent.

redox basis

If a substance doesn't have enough electrons, it will actively try to gain electrons through the oxidation process. Oxidation is a chemical reaction in which one reagent is oxidized (ie, electrons are lost to another reagent). Since substances with a positive ORP reading are seeking to acquire electrons, they are considered oxidizing agents.

On the other hand, electrons with an excess of ions can deprive the ions of oxidants without becoming unstable. Therefore, they are known as antioxidants or reducing agents. Higher or lower ORP readings (positive or negative) indicate a substance's higher oxidative or antioxidant capacity, respectively.

Why ORP Readings Are Important for Solution Testing

ORP is an important part of solution testing because it indicates how disinfected or contaminated the water is based on its oxidizing and reducing properties. For safe consumption, recycling or contact with our skin, water treated with a sanitizer has a higher oxidation potential, resulting in a higher ORP reading. By regularly monitoring ORP levels, it is possible to monitor the effectiveness of the sanitizer and adjust the water treatment plan accordingly.

Common Uses of ORP Meters

There are many reasons why someone might be interested in the ORP of a substance. Perhaps a common application is water testing for chlorinated swimming pools. Because the ORP of a substance is affected by all reagents present in the substance, ORP measurements are considered more informative than a separate pH reading that only identifies acids (hydrogen ions) and bases (hydroxide ions). Larger pools will often have embedded ORP sensors, while backyard pools that lack built-in monitors may need to be tested with a portable ORP monitor.

When you add chlorine gas to your pool, the chlorine gas gives up its own remaining electrons to neutralize or oxidize potentially harmful bacteria. Active chlorine electrons increase the ORP content of the water, thereby neutralizing pollutants. For chlorinated pools and spas, a safe reading for ORP is usually between 650 millivolts (mV) and 750 mV. As the chlorine breaks down and loses its oxidation potential over time, the overall ORP reading of the water gradually decreases. Although the level of ORP is generally related to the proportion of disinfectant in the water, ORP does not measure the level of disinfectant. Instead, the net oxidation and reduction properties of all reagents present are measured.

In addition to being used to monitor water quality in chlorination pools, ORP meters are widely used in the food processing and water treatment industries to ensure that water is free of contaminants and safe for recycling or consumption. Uncontaminated bottled or tap water has a positive ORP.

Adjust ORP levels

When it comes to swimming pools, ORP levels can often be adjusted by adding more active chlorine to the water to increase its antioxidant capacity. More sophisticated water purification systems may require a more sophisticated balance of total dissolved solids (TDS) in water to achieve a more favorable redox potential.