ORP Measurement of Pure Water

Pure water can take many forms. Pure water can be considered as either tap water, filtered water, or distilled water. In all cases, keeping track of the minerals in the water is essential to making sure the water being used is ideal for the application it is needed for.

 

Oxidation Reduction Potential (ORP) is a measure of the oxidizing or reducing activity in a solution, similar to the way pH is a measure of solution acidity or basicity. In water applications, the ORP indicates the tendency of a solution to react with mineral and organic impurities, including microbes. Measuring the ORP in water applications helps to determine whether corrosive contaminants are present and their concentrations. The ORP level for water disinfection is about 600 millivolts (mV) and the level for water sterilization is about 800 mV. Depending on where it collected, tap water ORP levels can range from  -200 to +600 mV in the USA.

 

ORP is important in pure water applications. For example, chlorine is one of the most common chemicals for pool water applications, but it must be removed in pure water treatment. Chlorine is an oxidizer—it will react by accepting electrons from other substances in the water. This is when ORP becomes important for making sure oxidizers such as chlorine or any other contaminants are removed in the water treatment process.

 

In cases where minerals must be eliminated to prevent unwanted activity in the water, distilled water is required. In filtered or tap water, certain types of contaminants or impurities must be removed depending on the municipal or state requirements. Whether it is distilled, filtered, or tap water, ORP measurement will be able to indicate the “cleanliness” of water.

 

The mineral content of the water will affect the ORP. Using ORP measurement in the water can give the tester an indication of the concentration of contaminants in the water, as well as the potential amount of activity in the solution.

 

An ORP electrode is constructed with noble metal—silver, platinum, or gold. Because noble metals are resistant to oxidation as well as corrosion, using these metals is best for water applications. When put into the solution, the metal will lose its electrons to the oxidizers in the water, creating millivolts. The noble metal of the electrode as well as the chemicals and contaminants in the water generates small voltages which an ORP probe uses to gather the ORP value of the solution. Since silver, platinum, and gold are different types of noble metals, each metal can give out different readings.

 

The S8000 series modular ORP platform is great for measuring ORP requirements in low ionic conditions. Low ionic samples such as pure water applications can cause ORP electrodes to appear drifty and unstable, making it difficult to use as a process control. For this reason Sensorex offers special models of our most popular electrodes such as our S8000CD-ORP-LC for use in low ionic conditions where the conductivity levels are less than 100 microSiemens.

 

To withstand the low ionic conditions of pure water, the chemistry inside the S8000CD-ORP-LC is balanced creating a ORP and reference cell well suited for these types of applications. The result is an electrode which is stable and repeatable which will allow users to utilize them for process control.

 

Another unique feature of the S8000 series is its cartridge style design with modules available for submersion and inline configurations as well as optional accessories for temperature compensation, ground loop interrupt, unity gain pre-amplifiers, differential amplifiers and two-wire loop powered blind transmitters.